One of my 3800s was doing this recently. It sounded right, but a tape would eject shortly after insertion. I just used some mild brute force. Next time I turned on the unit, I took my finger and placed it along the top edge of the drum, and gave it a gentle shove clockwise...
...and it started spinning.
After that, it was fine ... sort of.
It now squeals a bit. But that's another problem for another day. I just care that it works. It probably just needs lube. I'm not currently using it, and may never need to again. Mostly keeping it because it was the recording deck for about 200 of my S-VHS-ET recordings. Just in case I need the original VCR, for a stubborn tape, I have it.