[ujsf01]

My guess would be if there was no shim, this diff was not set up properly somewhere back down the line. Shims do two things, set backlash and side bearing preload. In all my years, I have never pulled a rear end down that was O.E. that didn't have shims in both sides. If one was missing, the carrier was probably walking slightly in the housing and also spinning the bearing race, which results in the groove you mentioned. You might be able to set it up correctly and postpone the eventual need to replace the damaged housing. Just my two cents worth. Rear axles are expensive and need to be set up right for longevity.