have my well tampered classic turntable and arm , square motor from the nineties , upgraded to black platter and arm. recently it started noticeable unstable and slower speed . it's like this for awhile. ordered and changed to a new belt . not sure if it helped, maybe a bit, but after some time it went back to same problem. can't know if the issue comes from the belt, or the motor, or other reason. read in some places about doing something to the motor spindle, but didn't understand it. other suggestion was to lubricate motor bearings , which i don't know where th y are. will appreciate any suggestion .