I'd be surprised if it was actually the bearings, especially if swapping out to an ovision worm didn't change the symptoms...but it is possible I guess.
This is the clutch issue I had:
http://www.helixgate.net/g11.html
http://www.helixgate.net/G11opw8.html
I'd be betting on the clutch or the gearboxes. There is some interesting gearbox tests and thoughts here.
http://www.helixgate.net/G11opw3.html