Most likely you snapped off the end that holds the gear in place and its not replacable. You must replace the whole mount plate motor but its not that expensive. But...depending where you broke it, I was able to fix mine as the plastic clip at the end broke and I took a small clip off a gear that was still stable without it and went macgyver on the gear tip. Once you put that little clip in place crazy glue the end to reinforce the clip. Use too much glue and your gear will get stuck from the glue seeping through and drying up. You can still spin it loose eventually but must turn quite a few times to make it turn nice and smooth again. Machine will sound a little different but it still works fine.
You can go to youtube if you replace the whole thing and find replace mount plate motor in AA Supply Videos.
You can go to youtube if you replace the whole thing and find replace mount plate motor in AA Supply Videos.