As a short term solution try this: Remove the platter and old belt from the turntable. Wet a Q-Tip with rubbing alcohol. Power up the motor to get the pulley moving and hold the Q-Tip against the moving pulley and clean both grooves (33/45) and let dry. Wet the corner of a paper towel sheet with rubbing alcohol and clean the surface of the subplatter that the belt rides along and let dry. With the same wet sheet, wrap it around the old belt and slowly and carefully clean said belt by pulling it through a few revolutions. Finally, put a small amount of baby powder or talcum powder into a small ziploc bag. Place the cleaned belt into the bag shake it enough to coat the said belt with powder. Take out the belt and shake off the excess, mount the belt on the pulley and subplatter and give it a go. Probably not the root of the problem but a good maintenance procedure and it would eliminate one variable.
-Matt