Shouldnt be too hard to rewind if its a 2/4 pole.
Sounds as though its single phasing, as in only one of the windings is working.
If it has start and run caps then I assume theres a centrifugal switch to switch over, have you checked this out, you could use a lathe to check it if you have access to one.
If it just growls then it looks like only one of the windings is pulling current, you need both on a permanent cap motor.
Have you tried new caps, cheapo's are not all that reliable in a demanding application like this.