Motors basically never lose our rpm that’s not how it works. They either run full speed or trip the overloads in a matter of minutes if not quicker. Probably better to just leave it alone unless the overloads are tripping. If you want to learn something new and you want to do something you could put bearings in the motor’s you can buy them at any parts store. Again though unless you have a loud noise or something I don’t think it’s worth doing. If you want to check them take the belt off the pump and run each one and see if any of them are louder than the others because there should be basically no noise except for the fan on the back of the motor. If they make noise replace the bearings.