Unbolt the caps and pull the carrier and see if there is any wear along the inside of the housing. Also inspect the housing itself. The wear on the back of the carrier would suggest that there is something either on the housing or the carrier itself that is making contact with the spinning parts. See the metal wear marks along the outer edges of the reinforcing ribs on the back of the carrier? You got something in there causing contact, the bolt heads stick out farther, so they took the bulk of the hits. The apparent even wear around all 6 faces would suggest that whatever it was would hit and turn each bolt to the next flat for a hit and turn on the next go around.
Be interested to see what you find when you get it broken down more.
Be interested to see what you find when you get it broken down more.