An update, just in case anyone else gets stuck with this:
The peg sits in the big space not the triangles. The peg pushes on the two flats, up on the left, down on the right.
The motor only spins one way. It can be reversed, but it doesn't to operate the central locking, so if you take it out, make sure you put it back in the correct way.
I stripped it all down, cleaned and lubricated it. Toothbrush works pretty good on the cogs, followed by a blast with an air line. I used silicone spray as a lubricant.
Put it back together.
Job done. (Apart from the other three solenoids I need to strip down