It may be that the bearings are dry. I had this issue.
You didn't specify but if it's similar to ours, Airxcel/Coleman, the motor has bushings with felt oil retainers. They dry out.
Ours stopped completely and fortunately, it didn't damage the shaft or bushings. To oil, I had to remove the motor, disassemble, drill out the rivets holding the bushings, clean everthing, and then oil and re-install the bearing retainers using screws.
If you're familiar with electric motors it's an easy task. Took about 45 minutes after the motor was removed from the AC. Most of that time was hunting the appropriate screws to re-assemble.
I think a replacement motor is around $125 on ebay, which is your other choice.