skywatcher Skywatcher Dob Synscan alt bearing jumping

[patm]

I've had the skywatcher 12" dob goto for a few years and I've dabbled with tuning up the bearings. I found the first year pointing was nice and accurate but the second year it went south. Adjusting the bearings fixed that up (they were slipping in both axis). I've been dabbling with photography using a DSLR and the results are often quite good with 20-30 second exposures but I keep getting an annoying jump in the altitude axis. What I can't figure out is the exact cause.

This mount has two encoders on each axis - one on the motor and one on the scope. When the clutch slips the scope axis and motor encoders mismatch so the controller kicks the motor to try and get them closer together. I figure this is what is causing the jumping.

What I'm not certain about is the cause. Do you think it more likely that the bearing is loose, letting the clutch slip or that the bearing is too tight, causing the clutch to slip until the controller gives the motor an extra shot, breaking free of the sticktion?