Fixing a Kodak Carousel slide projector

I was going through old family slides with the old family slide projector and noticed the focus motor was running continuously. I did some quick checks and verified that the bulb worked, but the mechanism wasn't moving. This is a known issue with these older projectors. I pulled the bottom off to have a look at the mechanism.

At least one problem was obvious: the plastic gears were crumbling (this being a common failure mode).

( the repair process (with pictures) )