Unstable Polarity on an Electric Motor

we're gonna need more info if you expect any sort of answer

Welcome to the forum

no sarcasm intended, just a statement of local operational fact

If you tell us things like:

model#

make, size & model# of the motor

date of manufacture

*

You will be much more likely to get the proper solution

otherwise you see what happens

a bunch of wild guesses

Yes, send this to a motor shop. If you want to keep this great piece of equipment running. And I sure hope you do! There are not too many of them around that I am aware of. Since you are only talking about the motor, I am assuming that the ways are still accurate and cut perfectly.

GA

I would just change the advice from "exactly the same rating and voltage" to the same capacitance and at least the same voltage and temperature rating.

AMF (who later became DeWalt) used cap start single phase motors for the most part, so yes, most likely your cap is failing; they don't last forever and if it sat around un-powered for years, the cap could be toast.