Pardon the intrusion. IIRC, the Panasonic/technics series of DD/TT drive systems are capacitively coupled to the coils? Thus on older tables (which they all are now), a thorough changing out of coupling and feedback electrolytic capacitors is generally required. Besides basic issue of the oil potentially being a fault point.
Ok, looked at the schematic. Not quite right, I was. IMO and IME, if oiling is fine, then my experience with about a dozen technics tables tells me that putting in all new electrolytic caps can refresh the operation back to what is that of a 'new' state. That the drive system's stability and operation, in the long term and in partial fault type situation, is generally tied to dried out electrolytic capacitors.
going back and re-reading the symptoms again, it definitely sounds like the electrolytic caps are dried out. That is the exact kind of behavior that happens with dried out old capacitors in a technics turntable.
The next thing that happens fairly soon after this.. is that the main drive IC can 'pop', due to the stressing.