I just completed this repair on a similar motor that had a stripped gear. That gear is a fiber gear that fails. Many motors from Williams or Gottlieb have similar gear trains, and I found that the fiber gear is the same. I had a spare motor for "parts" and swapped the fiber gear.

The problem is that the two halves of the gear housing are held together with hollow brass pins that are flared at each end. You need to drill out the pins, carefully separate the gear case, disassemble some gears, install the new fiber gear, lubricate as needed, reinstall the two case halves. To reattach the case I used flat head machine screws that fit into the countersunk hole, a lock washer and nut. Don't overtighten the nut or the shafts will bind.

For my repair I didn't have a clearance issue with the nut. It's not a difficult repair, hardest thing was locating the flathead machine screws of the proper head size and length. You may also need to countersink the case slightly to get the screw head to sit flush. Hope this helped.