Nikon D800 unexpected service issue: impact damage-replace mirror box

I finally sent my Nikon D800 out for service to deal with the well known AF issue. I initially received a service quote stating that the repairs would be covered under warranty. Today I received a second quote requesting authorization to replace the mirror box due to damage apparently caused by impact  (the AF issue to the tune of $375 will be covered under warranty).

This camera has never had an impact and the focus issue has been the same since day one. I have never seen any indication of oil leakage or anything else that would suggest a broken mirror box but I'm not sure what to look for. Does anyone know indicators of mirror box issues would be? Unless the camera was damaged in shipping I can't think of a possible scenario that would explain damage of this type and I'm not anxious to spend the $700 they are requesting for the repair. (Service description is listed as C (E) Service Repair Rank C.)