My Nell motor had been “fixed” in the past since the tabs were missing and the case was put together with electrical tape. When I ran just the motor with no load it would start in random directions, this makes me think that it is an asynchronous ac motor just like in your microwave turntable. That is why the turntable will rotate in either direction.
This is probably part of the reason why these units fail. The motor puts a lot of torque stress on the furthest our gear (plastic outer gear or last bronze gear) and that’s why those both fail. I asked my EE brother if there is a way to force the motor to run in only one direction and he said without a starter winding, you can’t.
The problem with mine was the plastic gear was loose on the knurling shaft so some epoxy fixed that. I still need a new o ring because the saw blade slips.