I haven't disconnected it but your suggestion did give me an idea. I loosened all the screws assembling the motor mount/coupling and gradually tightened them evenly while checking the rotation. That cleared the tight(er) spot and it is now even easier to turn by hand with the motor disconnected. So easy, in fact, that I can't believe that any self-respecting motor of that size wouldn't eat it up and spit it out.

In fact it does turn the table now well enough for me to complete the job I was doing. I only need to turn the table between cuts (not while cutting) and it managed that except for some missed steps at one stage which let me know that it's still marginal.

I'll swap out the driver when it arrives and try it with this and a replacement motor.