Good news: the Zap-a-Gap glue seems to have done its job and after a few applications the crack has been completely filled. No photo, since it looks almost exactly the same, there's just a slight shine from the glue when it catches the light. It's not a very high stress joint (usually!) so with a little care I don't expect any more problems.

Quote Originally Posted by Kup
How did it happen anyways? First time I hear of this.
Yeah, it was totally my fault. I was converting him back from combined mode and applied too much torsional stress to the hinge. There's a grey latch on Mobile crane to help keep the two halves together in combined mode. It's pretty flexible anyway but you have to bend it quite a bit to detach. To lessen the stress on it while detaching I twisted the crane halves apart a little as well. It seemed like a good idea at the time but I wasn't thinking about where all that stress would end up - in the hinge attachment point. The plastic is quite hard so there was very little movement until the plastic suddenly gave in and twisted.

Anyway, lesson learned: Flexible plastic is for bending.

For anyone who needs to apply glue to small fiddly bits, there's a good modeller's trick that's equally applicable to toy repairs.

Rather than squeeze glue direct from the bottle onto the part, squeeze a drop or two onto a non-porous surface like a ceramic tile or an old plate. I use glass microscope slides but bottle tops or even greaseproof or waxed paper might work. You can then dip a sewing pin or toothpick into the puddle of glue and pick up a small bead of glue, which you can then apply to the part, giving you much finer control over the amount and placement of the glue. If bits are completely snapped off you can even dip the end directly into the glue puddle for an even coat.