TR electric window motor disassembly

I've removed the electric window motor/gearbox assembly on my 90 TR for an overhaul. The windows were slow, and the problem seems to be the bearing on the main sprocket wheel, where it locates into the base of the casing. Has anyone taken this unit apart? Having removed the 3 chromed screws and cover then disengaged the pinion, the sprocket wheel can barely be moved. I can't see how the bearing comes apart for overhaul? Any help would be appreciated.

Steve