Rubber teeth broke off drive coupling.

Using information from other users, I pried/ripped the rubber portion off the drive coupler, leaving the aluminum disc base exposed. I did not have a thin flat wrench of the right size to hold the drive shaft, so I wound up carefully inserting the wrench into the motor to keep it from turning while I loosened the disc with pliers. Once loosened, it was easily unscrewed, and the new coupling screwed on.