Probably hardened lube around the bearing areas. Try some CRC or WD-40 at the driveshaft and let soak in then spray again and leave it sit for about an hour.
These are easy to service by removing the topside screws, making it easy to access the motor for a test. It's been many years since I dismantled one of these, but take note of the motor's orientation in case it matters for polarity's sake.
