I think I've returned Hj motors for rebuild 5 or 6 times after seizing internally. One motor I had seize after one season. Had it repaired and midway through the next season it was seized again. Hj motors have a water intrusion problem that I don't know if they have ever fixed. I store my camper in a carport these days and I haven't had any problems since. I also picked up a spare motor so it may just be a Murphy thing. Now that I have a spare I won't have any failures. The first couple motors I returned they suggested wrapping a plastic bag over the motor head to protect it from the weather. Pretty poor design for a part that is expected to be used outdoors.
In case the motor is just sitting on a dead spot, you can try using the hand crank with the motor still engaged and see if that frees it. Didn't work for me but YMMV.