Update: There is too much friction for the motor to turn. I don't know what to do about it yet.
The two smallest gears in the Capsela worm gearbox seem to break a lot. This includes replacements for them. It also includes a slightly larger replacement for the spur gear that interfaces with the worm, to make for less play. The result of the latter replacement may make things too tight, though.
My printer has sloppy tolerances. You will probably need to tweak sizes for your printer.
I haven't found a good way to open the gearbox. I ended up cutting it with a rotary tool and gluing it back, which was ugly. If you know a better way, tell me.
This is just a remix of this gear library.