Repairing One of Those Pesky Broken RAH Shoulders

Hello, everyone!

It has been a looooong time since I posted here, but I assure you, my return isn't motivated by frivolity. No, ladies and gentlemen. This time I'm on a mission.
An important one.

Today I will be repairing none other than

this dismembered Plastic Torso!

No, seriously...

The torso used to be a part of Medicom RAH (actually "Real Action Heroes") Roy Mustang, but as you can see, the shoulder is broken. Roy's broken parts were graciously replaced by Medicom Toy a couple of years ago, but I'm going to be fixing the broken shoulder on the left-over torso anyway.
The reason is this guy:

Meet Medicom RAH L.

I get a lot of weird questions about a lot of weird figures, but this guy tops them all. I've had more questions about RAH L than any other figure.

To sum up, your standard RAH body has approximately one zillion Chinese-puzzle-box-like moving parts, which makes them delicate to start with, but some of the older RAHs like L go beyond mere delicateness – after a while, the plastic around their joints actually starts to crumble of its own accord.

This means that one day you're happily going about your business when suddenly your most beloved, most prized, most expensive action figure's ENTIRE ARM just FALLS OFF.

FOR NO REASON.

I've said it before, and I'll say it again: *HYSTERICAL SCREAMING*

This – along with accidental decapitation – 

Oopsie

– is the most common RAH problem people ask me for help with. And I know my readers aren't making it up, because this is exactly what happened to my RAH Roy Mustang (after I put his head back on), and it is MIGHTILY DISTRESSING.

Don't feel ashamed for crying, ladies and gents. You're not alone.

So, short of replacing the parts, what can we do about it?

Answering this question took a fair bit of experimentation, but – EUREKA! I finally found a satisfactory solution.

This is where it gets Technical...

The main cause of all the anguish is this thing:

The Thing, shown here next to a tiny washer.

This peg used to hold the shoulder on, but now it doesn't because the cone of plastic it used to be embedded in has disintegrated.

But what's so bad about the peg itself?

At first glance, it seems rather like an innocent-enough screw, but look carefully at the shape, and you will see that it is actually an itty-bitty-super-fiddly RATCHET. The only way this ratchety little S.O.B. could have been inserted in the plastic in the first place is if the shoulder-plastic was heated until it was soft (or it could have been done with a tonne of pure, unadulterated force, which you'd think would break the plastic, but I could be wrong).

Now, I'm reverse-engineering all this, so I may be mistaken, but I'm guessing that pushing this knobbly chunk of metal through the hot plastic is probably what weakened said plastic in the first place and later went on to cause the infamous crumbling we all know and love.

So here's the question:

How the heck can we get the peg back in!?

The answer is:

We can't.

The plastic which used to hold the peg in place has now crumbled away, and even if it hadn't, the temperatures required to heat PVC to a point where it's soft enough to work are not all that convenient (and now that the plastic is a few years old, a tonne of pure, unadulterated force would definitely be out of the question).

So I'm going to show you how to modify a screw to act as a replacement shoulder-peg.

NOTE: READ ALL THE INSTRUCTIONS BEFORE YOU BEGIN!

You may want to have the broken pieces with you, so you can see what I'm talking about.

--- EQUIPMENT YOU WILL DEFINITELY NEED ---

1. Needle-nose pliers

2. One (Self-Tapping) Screw (approx 2mm diameter)

3. A Ruler

4. A Hot Glue Gun OR Epoxy Putty

5. A Pin Vice

8. 2mm diameter Drill Bit

9. A Regular Size Phillips Head Screwdriver

10. A Small Size Phillips Head Screwdriver

--- EQUIPMENT YOU WILL PROBABLY NEED ---

11. Sandpaper

12. A Big Sewing Needle

13. Scissors

14. Forceps

15. A Hairdryer

--- EQUIPMENT FOR PEOPLE WHO LIKE "EXPERIMENTING" ---

16. Bandaids

Part One: Replacing The Peg

First of all, get the metal peg out of the shoulder. You can do this by pushing it from behind (on the ratchety end) and then wiggling it out with pliers.

It should have a small washer on it (pictured above). Keep that washer safe. You're going to need it later.

NOTE: There's a possibility that the shaft that contains the head of the peg will be covered by what I'm going to call a "blocker". These are put in place for aesthetic purposes, but for us tinkerers, they're just in the way.

Blockers are made from soft plastic and not usually glued in. I personally remove them by stabbing them with a big-arse sewing needle and prising them out like so:

Note that the blocker in the photo is covering a screw, not the peg, since
my dismembered torso's peg-blocker was already removed.

With the blocker out of the way, you're free to remove the peg.

OK, now you've got that pesky peg out, the trick will be finding a screw which is about the same width as the original peg, but – and this is important – a few millimetres longer.

It was while pondering this that I realised I had kept a packet of small screws in my desk for the last five or six years for no reason.

*GASP* Could it be!?

Oh yah!

Had I not been so lucky, I could have just taken the original peg to the hardware store and compared it to the screws they had for sale until I found one with the SAME SHANK WIDTH.

Don't worry about the width of the thread, it's the shank which must match the original peg.

And speaking of the shank, make sure it is AT LEAST 10mm long (11mm is better). This is not including the head. You can see in the photo that the shank of the screw I am using is about 14mm long.

Anyway, something you may have noticed about the screw in the photo above, is that it is not only longer than the peg (good), but it also has a conspicuously wider head (BAD).

The reason this is bad is because the screw-head must fit down the narrow shaft from which you have just removed the original peg. What's more, it needs to be small enough to rotate freely within the shaft.

The shaft in the shoulder part. You can see by the comparative
hugeness of my thumb that it's very narrow. (If you're wondering why
 the edges of it look so mushy, my advice is to be careful with the pliers.)

If you managed to find a tiny-headed screw which fits down the shaft, good for you.

For everyone else, there's sandpaper.

Get a piece of regular woodworking sandpaper and file down the screw head, rotating it frequently, until it's small enough to fit down the shaft. This will take a little while, but it's overall not that difficult.

There will be some metal dust, so you might prefer
to do this outside.

Luckily, the screw doesn't need to be as insanely narrow as the original peg. Here's how the modded screw looks compared to an un-modded one:

Now you can put the tiny washer on the screw and fit it down the shaft.

You may find, as I did, that instead of rotating freely in the shaft, the screw threads bite into the plastic in the hole at the bottom of the shaft.

Instead of going around and around, in screws in and out.

This is a very tedious problem, but it can be fixed with some more tedious sandpapering.

The problem this time is the screw-thread.

Notice how the original peg is smooth at the top end, under the head?

Well, now we have to recreate this (roughly). Now we get the pleasure of REMOVING THE TOP 2-3MM OF THE SCREW-THREAD WITH SANDPAPER.

yay

There are probably a bunch of ways of doing this, but here's how I eventually managed it:

1. Cut a very thin strip of sandpaper. About 3mm wide.

2. Using forceps, make a noose for the screw with the sandpaper, like so:

Note the position and orientation of the screw-head with respect to the forceps.

This will hold it in place while you enact step 3.

3. Pinch the sandpaper tightly against the screw-thread and, using an appropriate screwdriver, turn the screw around and around until the sandpaper looses its bite.

Pinching the noose.

4. Undo the noose, move the sandpaper along a bit so that a nice fresh, abrasive part of the paper is in contact with the thread and repeat steps 1 - 4.

This process will slowly grind down the top of the screw-thread until it no longer bites into the plastic. You may have to repeat it quite a few times (I know I did!), but it works.

And luckily, you don't have to grind the thread down to nothing before it stops biting.

Here's what my peg-replacement looked like after sandpapering:

Not nearly as smooth as the peg, but it still does the job –
IE It turns around and around in the shaft.

The tiresome screw in the tiresome shaft.

Alright, so now the replacement peg fits down the shaft (with the washer in place!), and can rotate freely!

We must be done, right?

Wrong.

The next problem is the length of the screw shank. (Sigh)

This must not exceed 11mm, and, as I mentioned previously, the shank of my shiny new replacement peg is a whopping 14mm.

Luckily, there's an elegantly simple method we can use to get that shank down to size!

yay

Be sure to measure the length of the screw shank every once in a while between bouts of merciless sandpapering. When you've finished, it should be no more than 11mm in length, but no less than 10mm.

That doesn't leave very much room for unchecked merciless sandpapering error.

Once again, I will stress that the 11mm length refers to the SHANK ONLY! It does not include the head of the screw!
(For the purposes of this project, I couldn't give a rat's arse how deep the screw-head is.)

OK! Done!

The shiny new replacement peg can now fit down the shaft (along with the tiny washer), rotate freely within the shaft, AND it's 11mm long!

AT LAST. AT LONG LAST, we are finished modifying the screw!

Now, on to ––

Part 2: Modifying The Shoulder Joint

yay

The broken plastic shoulder joint is made up of several fiddly pieces.

In this section, we will be dealing with what I'm going to call the Arm Part and the Fiddly Plastic Washer.

The arm part. This one looks particularly bad because I once tried to replace the crumbled plastic with yellow epoxy putty.

The Arm Part is probably attached to the rest of the arm in your case, and it contains the thing which is actually broken. As far as I can tell, where this ugly mushy break now sits, there once used to be a cone-shaped protrusion into which the shoulder-peg was inserted. This is, of course, now completely obliterated.

The Fiddly Plastic Washer. Note that it is different on each side. One side is concave (left), the other is flat (right).

The Fiddly Plastic Washer fits over the round depression in the Arm Part, with the concave side facing down:

Just like this. Note how it makes a little sort of cave.

In this section, I'm going to be filling up the little sort of cave made between the correctly placed Fiddly Plastic Washer and the Arm Part with hot glue from a glue gun. (You could also use epoxy putty, if you like putty.)

After the cave is filled, I'm going to drill a hole through the centre so that the new shoulder peg can be inserted.

Step 1:

FOR GLUE-USERS

Fill the empty space with hot glue.

This is pretty simple. Just squeeze the glue in gently until the hole is full. If you accidentally use too much glue, scrape/wipe off the excess until the surface is relatively flat (I used the big-arse sewing needle to smooth off my excess glue).

When you're done, it should look more or less like this:

FOR PUTTY-LOVERS

If you're using epoxy putty, knead it up as per the instructions, then press it onto the broken surface of the Arm Part in a small lump.

Next, push the Fiddly Plastic Washer (concave side down) firmly over the putty-lump. This will mould the putty into the desired cone-shape.

Smooth off the top surface and remove any excess putty from around the edges of the washer with a craft knife or other scrapey tool of your choice.

Step 2:

This one's nice and relaxing: set your work aside until the glue/putty has set.

If you used putty, read the instructions to see how long you should wait, then add a few more hours to be safe.

If you used hot glue, then you just have to wait for it to cool down to room temperature.

In my case, this took long enough to have tea and crumpets and purchase some new laboratory glassware online.

I don't know what all the "popular" kids are doing with their lab glassware
these days, but I like to culture primitive land plants in mine.

Step 3:

In the Arm Part, there is a screw which runs perpendicular to the direction of the vague hole where the shoulder peg once was.

Before you do anything else, remove that screw.

It may be covered by a plastic blocker, but you can easily prise that out, as described earlier in this article.

Note that the screw is quite small, and you will probably need a small Phillips Head Screwdriver to remove it.

Once you remove the screw, you will be able to separate the shoulder part (which contains the break) from the rest of the arm (which in my case is dismembered).

This will reveal a brand new narrow shaft in the broken part.

It shall henceforth be affectionately named "The Second Narrow Shaft".

I just love narrow shafts, don't you?

Step 4:

Using a pin vice and a drill bit the same width as the screw-shank (in my case this is 2mm), drill a hole straight down through the middle of the glue/putty filling the Fiddly Plastic Washer.

The screw shank (not including the thread) and the drill bit are the same width (2mm).

Friendly neighbourhood pin vice, with the 2mm bit installed.
You can buy these at hobby stores, some hardware stores, and on eBay.

The above photo is an attempt to show (more or less) the angle you should be drilling at. At the bottom of the plastic part is the glue/putty filled washer.

Please note that the screw is shown in place in this image -- this was a MISTAKE! TAKE THE SCREW OUT BEFORE DRILLING!

This photo (directly above) shows the hole drilled through the middle of the fiddly plastic washer. Mine is a little off-centre, but it still worked.

Once again, note that the arm is still attached in this photo. This was a mistake on my part. When you drill the hole, remove the arm first.

Drilling can be a little tedious, because the bit will most likely keep getting jammed with plastic debris. Every time this happens, just pull the bit out of the hole, clear it off and press on.

Keep going until the drill bit comes out through the wall of the "Second Narrow Shaft".

NOTE: Drilling half-way is no good. I've been there, and I can tell you that neither hot-glue nor epoxy putty is strong enough to hold the replacement peg (or the original peg) on its own. You must drill through the plastic as well. The glue/putty is just there to add a bit of much-needed extra friction.

AND THE SHOULDER IS DONE!

Part 3: Assembly

This is the last and thankfully easiest part of the whole saga.

First of all, make sure the tiny metal washer is fitted onto the modified screw like so:

And then insert the screw and washer into that annoying narrow shaft I talked about so much back in Part 1.

This again.

Now get your trusty normal-sized screwdriver and screw the modified-screw-cum-replacement-shoulder-peg into the hole you just drilled, reattaching the repaired shoulder to the torso.
Make it tight enough that you can work the previously-broken shoulder joint. The joint should feel reasonably firm, but not stiff. Remember, you want the figure's arm to move easily, but be firm enough that it doesn't fall down under its own weight.

Now some double-checking:
Looking through the drilled hole in the wall of "The Second Narrow Shaft", you should just be able to make out the tip of the replacement peg.

In most cases, these parts would still be attached to the torso.

If the peg protrudes into the shaft, take it out and sandpaper it until it doesn't.
If the peg is allowed to stick out into the shaft AT ALL, then the shoulder won't work properly. If you measured carefully earlier, then you probably won't have this issue.

Note that the less times you insert and remove the screw, the better, because each time you do, the joint becomes a little looser and more fragile.

Once the replacement peg is safely in place, all you have to do is slot the shoulder joint back together, do up that little screw you removed earlier et voila!

THE SHOULDER IS FINALLY REPAIRED!

Yaaaay! The dismembered torso is slightly less dismembered than before!

At last! At along last!

Okay, now that it's fixed, a note on maintenance:
The replacement peg is fairly likely to come loose with time and shoulder-use. For this reason I recommend treating the shoulder extra carefully. However, if the joint does come loose, tightening the peg with a screwdriver should fix it.

*dusts hands*
That was the most complicated article I have ever written!
If you have any questions, feel free to ask me down in the comments section!

As always,
Good luck with your repairs!

     Cheers!
          Sparkey

Generic Action Figure Repairs - Two Methods to Fix Most Breaks!

Greetings!

So I've been looking at my stats recently, and I am getting a lot of refers from people looking for info on fixing broken Figmas.
I haven't actually managed to break any of my Figmas yet, but they're not so different in the way they work to a lot of other figures, so here I will be explaining two methods of repairing figures which are applicable to almost all PVC toys (including Figmas!) and can probably fix over 90% of breaks!

OK, first up, I'll explain the difference between a low stress area and a high stress area:

Low stress areas are not put under much pressure. They're usually not moving parts and if they are, then they're only moved minimally.
If you want to fix one of these, read Method No.1.

High stress areas are the things which break most often. They're things like shoulders, knees, necks, elbows, hips, etc, which have quite a lot of stress put on them when the figure is being played with.
If you want to fix one of these, read Method No.2.

Method No.1 – Supa Glue
For low stress repairs.
This is a really good (and DUH obvious) method for visible areas which are not part of a moving joint. It would be great for non-posable scale figures, snapped accessories (like swords or firearms) or other small things.

The example figure I will be repairing is Nendoroid Millhiore F. Biscotti!
Isn't she pretty?

Unfortunately, just after I got her, she fell of her horse... er... bird... er... mount and her ahoge broke where it attaches to her head!

Ahoge means "foolish hair" in Japanese, and, if you didn't know already, that's the silly bit of hair sticking out at the top of her head.

In Nendoroids, large ahoge like this are actually posable! You can rotate it from side to side so it can point in any direction (I love Nendoroids)!
I would not recommend trying to fix anything which will be put under higher stress than this ahoge with glue alone. I'm careful when I'm posing it now, but it's been a few months and it hasn't broken yet.
I didn't take any pictures of it when it was broken because it was before I started this blog, but here's a shot of how it looks now:

You can see the break just above where it attaches to her head.

Anyway, after freaking out and practically crying (she is nothing without her ahoge! NOTHING, I tell you!) I glued it back on with supa glue.

This is very easy.

Just put glue on the broken surface and then push the two parts together until the glue grabs. This usually takes about 30 seconds or so.

If it doesn't grab the first time, it probably means you used too much or too little glue. Don't be discouraged if you have to try this a few times with different amounts of glue... oh yeah, and don't get the glue on your skin because it sticks to people :O

Note: Supa glue only works on really clean fractures, so if the plastic around your break is a little mushy, you might want to try a different adhesive. For info on choosing the right one for the job, have a look at my glue info page.

As you can see, the supa glue worked a treat on Princess Biscotti. Her ahoge is even still posable!

Look at that ahoge go!
(This looks way better when you're listening to fast music)

Another example of where this method is really useful:
Figma Marisa's cup had come unstuck from her hand and needed to be re-glued.

And that's Method No.1.

Method No.2 – Drilling & Pinning

This is my personal favourite method for fixing high stress fractures: this includes action figure joints! YES, THAT MEANS FIGMAS!

The equipment required is not necessarily the kind of stuff that everybody has lying in their desk drawers, but if you're a figure collector, these tools are an invaluable resource and well worth the small amount of money you will pay for them.

All of these things are easily obtainable from hardware stores, hobby shops and online!

This is the method I used to fix RAH Roy Mustang's broken head, which you can read about here!

For now, however, the figure I will be demonstrating on is Pure neemo Kanata Sorami!

Poor Kanata. Her knee joint popped out and so I took off her boots and trousers to fix it, but in doing so, I broke her foot off! *facepalm*

Even though she can still stand with the foot off (I just jam her leg into her boot) I wanted to fix it, because she's just not the same with an amputation.

Here's the busted foot and the ankle it's busted off:

The foot snapped off at the ankle joint.

Pure neemo ankles are extremely similar to Nendoroid and Figma joints!

Something like this is way too small and gets put under way too much strain to be fixable with glue alone, so I'm going to drill a hole in each side of the joint and insert a bit of wire before gluing.

Here is Kanata with the tools I will be using:

Anticlockwise from top: 1.25mm wire, pin vice with drill bits, a suitable adhesive for mending PVC,
wire cutters, pliers, a 1/6 scale designer Bauhaus chair for Kanata to sit in while I work (optional).

To start, drill a small hole into the fractured surface on each of the ankle and the foot. The holes should be roughly 3-4 millimetres deep (for my empirical friends, that's about 1/8") and the drill bit you use should be the same width as your wire, or as close as possible. My closest drill bit is 1.3mm and that works fine with the 1.25mm wire.

Me using a pin vice, in case you were wondering what it does exactly. It's
basically just a little handle for a drill bit.
(My hands aren't usually purple – I have eczema and it's cold.)

The foot, after drilling.

Notice, in the above picture, that there is a centreline in the joint. This is not a mould line. It is the juncture of two separate pieces of plastic. It is the movement of the two pieces against each other which makes the joint functional.
Also notice how the hole I drilled does not go directly through the centreline, but instead to one side of it, through the original broken surface.
If you glue a wire through more than one of these pieces of plastic then the joint will be frozen and will not move anymore!
It's exactly the same deal with Nendoroid and Figma joints.
In fact, here's an old Nendoroid joint which has been taken apart, so you can get an idea of how it works:

The hole in one piece fits over the central peg in the other. This allows
the two pieces to rotate around each other – simple, but very effective!
Many joints are constructed this way.

Here is the ankle after drilling:

If the end of the peg is really mushy after drilling, just neaten it up a bit
with pliers and a craft knife/wire cutters so that the joint will fit
together nicely when gluing... this picture was taken after neatening.

Notice how the hole is slightly to one side in the above photograph. This is to correspond with the fact that the hole in the foot is also off-centre. If you can't get this quite right, it's no big deal, but it's better this way.
... Actually, to be honest, I was hoping to pull the peg out of the leg part before drilling to make it less awkward to get to, but the pliers didn't grip properly and I just ended up mashing the peg :/

Of course, this method is not limited to this kind of joint. You can use it to fix all sorts of things, like this fracture, in the straight shaft attaching RAH Roy Mustang's neck to his body:

This was successfully fixed by drilling and pinning
and Roy has since been posed many times over.

Anyway...
Now that the holes have been drilled, it's time to cut a piece of wire to fit them.
The length of the wire should be equal to the combined depths of the drilled holes.
For example, if I drilled a hole 3mm deep in the ankle and 4mm deep in the foot, then the wire will have to be 7mm long so the whole joint fits together nice and snugly.
It is advisable to cut your wire to the right length before gluing anything. Believe me, it's just easier that way.

Once you've cut your wire, glue it into one part of the drilled joint and let it set for a few hours.

Kanata's foot with the wire glued in. The bent wire in the foreground
was used to spread the glue.

Now that the glue is at least partially set, apply more glue and glue the whole joint together... with glue (I really love glue, don't you?).

This is how the joint looks now that it has been put back
together – it looks a bit messy close up, but from a normal
distance you don't notice it much.
It's certainly better than having no foot!

Figma Chie has come to look at Kanata's foot while the glue is drying.
She makes a pertinent (if dry) observation.

Now wait for the glue to dry. I don't know how long this will take. It depends on the type of glue, the temperature, atmospheric conditions, alignment of the planets, etc...
Make an educated guess based on the instructions on the packet and add a few hours. That's my advice.
...
   ...
      ...
OK, so the glue is now set and... did it work?

Heh. Sorry about the lighting... I think a cloud must have come across
when I shot some of the frames...

Yep.

And that's Method No.2.

Well, that's all from me!
I hope this helps some of you guys with your Figma-related problems!
Cheers! Sparkey.

Fixing the Central Torso Joint of a 12 Inch action Figure

Hello, all!
Gees, it's been ages since I posted here!
But that is for the simple reason that I have miraculously not broken any of my figures for that entire time (not even Roy)!
... until a couple of weeks ago...

I was playing around with RAH Captain Harlock (the more recent version, not the super old one) when suddenly something went "crack". It's the kind of sound you never want to hear any kind of action figure making, let alone your pricey discontinued 12-incher.
Captain Harlock is now fixed, but I spent, like, an hour getting him into a really cool pose (you know how it is) so for the duration of this blog, I will be using a different model.
Meet RAH Ginko.
He looks a bit apathetic, but he's actually a really helpful chap, and today he's kindly agreed to be an example RAH body for us.

Although the captain didn't seem visibly broken at first, as I continued trying to pose him, the joint in the middle of his torso became mysteriously limp, meaning he was unable to stand straight and, on further inspection, his entire top half could now be removed from his legs (which really isn't normal).

The problem joint, circled in blue.

A normal, upright pose.

When broken, Captain Harlock could
only slump forward like this.

One of the few photos I took during the
captain's operation.

Ouch.
Now, RAHs are complicated things, and I have to admit that what actually broke is still a mystery to me. I couldn't see any obvious breaks, and if anything fell out without me noticing, it must have been practically microscopic, because I searched all around the floor afterwards and I couldn't find anything.
Still, based on a theory I developed after several blunders, I managed to fix the cap'n.
So, the first thing I did after I broke Harlock was take him apart to see if that would shed any light on the matter.
First thing's first, the screws needed to come out.
RAH screws are nicely hidden under little round bits of plastic, but these can (usually) be easily removed with a pointy thing like a very small screwdriver or a knife.

Observe the five covered screws in Ginko's back.

I decided to undo the upper torso part first, since that was where I thought the break had occurred, but after fiddling around with several confusing pieces I realised that, in fact, it was the lower torso which had broken (the tipoff was when I realised that the body was no longer connected at the waist).
I then went to unscrew the screws in the lower torso, but Medicom has for no apparent reason filled the screw-heads in with some sort of paste which is extremely hard and resistant to several very good solvents, so I couldn't take apart the lower torso and had to peer in the hole at the bottom of it instead.
What I saw was a... spring.
A spring?
It seems to be part of a suspension system which gives RAHs their solid feeling whilst also having that awesomely flexible mid-torso joint... I think.
To explain better, here is a diagram of what roughly I think is inside the lower torso of a RAH body, based on what I could see:

The yellow thing at the top is part of the mid-torso joint.
It runs along tracks in the upper-torso part, allowing the torso to bend
back and forth. The yellow thing is held down by the spring (green),
which is, in turn, held down by the central peg attached to the legs (black).
The red thing can move up and down in the central shaft (blue). When the spring
is not held down, the red thing can move more freely, the yellow thing becomes
lax, and the torso becomes loose and slumps forward.
I hope you could follow that... it's hurting my brain trying to think back.
The grey blob is where I couldn't see. Sorry for the crappy drawing.

The spring seems to regulate the stiffness of the central torso joint.
The tension on the spring, in turn, is regulated by the vertical position of the sticky-outy bit on the central peg (black) within the spring coils.
When the tension on the spring is wrong, the figure slumps.
I think it is the theoretically existent sticky-outy bit which broke off, because there was no such thing visible by the time I took Captain Harlock apart and such a thing would be needed to make sense of the mechanism I could see inside the lower torso.
It would also have to be extremely small, which could explain why I couldn't find anything which could have broken.

A closeup of the broken peg (and the top of the captain's trousers);
if you look carefully, there's a smudgy area on the front of the peg
where something could have broken off.
Click on the image to enlarge it.

So to fix it: I drilled a hole into the central peg on the smudge and pushed a tiny itty bitty short piece of wire into the hole, making a new sticky-outy bit.

I drilled the hole using a pin vice, which
I finally got around to buying.
Use a drill bit the same width as your wire,
or as close as possible.
The wire I use has a 1.25mm diameter.

I then put the torso on backwards (you have to put it on backwards because that's the only place there's a gap for the sticky-outy thing to fit through) and turned it around fully several times as if I was screwing on the lid of a jar. Something made a satisfying noise and suddenly, miraculously, Captain Harlock was back to normal.
I didn't even glue the bit of wire in, because I was just testing a theory, but once fixed, he didn't want to come apart again, so I just left him that way. (That's why there are no photos of the fixed part or the underneath of the torso.)
Anyway, so yeah. Captain Harlock is fixed and I hope that made some kind of sense and wasn't too confusing. Even I am still a little confused.
If you have the same problem as I had and something here doesn't make sense, please feel free to email me for clarification: sparkeydavis@yahoo.com

well! My post is at an end!
As always, good luck with your repairs!
Cheers! Sparkey