Hi,
My two cents:
I wonder if it hydraulic locked on the Marvel Mystery Oil?
I would pull the plugs and leave them out. (cover plug holes with a rag)
Drain the oil and refill with clean.
Turn by hand, not the starter, and see if you can get the whole 360 rotation
Could also have some mouse or squirrel's stash in one of the cylinders too.
Good luck!
