Based on the wear pattern on the back of the pump it looks like the bearing (Chinese?) probably went bad and the defuser ring got knocked off. I had that same thing happen on my Dodge diesel. Pump was leaking pulled it off and noticed that the new pump had a difuser ring but the old one did not. Went back to the parts store and they started calling around to some of the repair shops they supply to. They answer was " when the bearing starts to go bad, the shaft moves, and the tolerances are so close the the ring starts to get ground off the pump. All the chips or chunks end up in the block. Hopefully not to be heard from again.