Hey Brian, I have a bearing service manual and troubleshooting guide. In that manual it shows bearings that are like what you describe. It can be caused from lugging the motor. You mentioned you towed heavy loads with it. Do you recall lugging it much? I guess it can happen with or without a towed load. Anyway, I thought I would post that. Lugging can cause you to scrub bearings into the under lying babbit material...A.T.