Hi Grant. The bearings that take a hit when the telescope is accidentally knocked are the 22mm dia ones both ends of each slow motion axle. The mount was designed with roller bearings in these positions and they do not cope well with large sideways forces. On the mounts we (AWR) have serviced ther ehave been distinct dinks on the rotation of some of the bearings we have removed. These must run smoothly else you will get unexplained jumps in the tracking especially visible in CCD work. I would not bother changing the large bearings on the primary axles. Certainly I would clean out the old grease. It is a magnet for contamination.