Just a thought, but have you checked the four transmission bolts under the bike? I know of one case where these all vibrated out/loose. Should be easy to check on a Ridgeback. Gotta drop the rear of the shocks of a K-9 to access them.
The first alignment for your transmission is to bolt it to the primary. If the transmission can move against the frame, maybe that could produce enough flex to ruin seals/bearings and grind on the case?
And---Barnes does install a higher quality of bearings than stock in his rebuilds.