Rotel Turntable speed

I purchased a Rotel RP-2500 turntable used and it won't keep a constant speed. I've searched the web and tried all the suggestions I could find. New belt, cleaned pots, greased spindle, and replaced (what I assume to be) the DC filter capacitor. The fluctuation in speed seems to follow a pattern (if that makes sense) - as if it slows down and speeds up at the same platter orientations each revolution. Could the platter be bent? I don't know if it's an electrical or mechanical problem at this point. Any clue if that motor can be substituted? Any other suggestions before I get rid of it? It's a good table otherwise...

Thanks