Were you able to get it fixed? I had pretty much the same problem with one I’m working on and figured it out.In my case the switch on the bat unit that makes the motor run was too closely adjusted and with the old loose worn out parts,the motor would run an extra fraction of a rotation causing the switch to close again.I’ve had this happen with some old pinball score motors as well,when the get old and loose,sometimes the motor doesn’t stop immediately and then it keeps rotating after it closes the run switch again.