What has probably happened is that the old oil in the motor bearings has turned to sludge from dirt and heat. You will need to remove the motor (probably three spring clips that love to fly away), disassemble the motor by removing the upper and lower bearing retainers, and carefully work the bearing retainers off the rotor shaft.
Then soak the bearing retainers in lacquer thinner, clean up the rotor shaft, relubricate with Zoom-Spout Turbine Oil, and reassemble. You will probably find that the motor mounting grommets have turned to dust and will have to be replaced, as will the rubber-tired idler pulley.
You will then find that the crystal cartridge has perished from age and humidity. It can be rebuilt by West-Tech Services at www.west-techservices.com
or a newer replacement can be installed.
Motor grommets, idlers, and cartridges are available from Gary at www.thesoundofmusic.com