Easy fix...

on the round part that has a square hole through it... tap that through the other side of the gearbox... file the crimped parts of the base of the gearbox to remove the 1mm ali cover plate...

Once uve done that you sould be able to nock out the shaft totaly with the gear and bushes...

Replace the shaft with a square hole with a solid bar of the same OD... re-build the gearbox, with bushes then pin through the boss on the nylon worm wheel into the new solid axle....

..bore out the pulley and fit it over the new solid shaft... then pin/grubsrew it on.

Something ive considered doing, as its probably a 30min job per side if you have a bar the right OD kicking around, and it can be done in the shed/garage without the need of a lathe.

Hope this helps.