When you have a warranty they are stating that the car will be able to perform on the roads given normal road conditions. Normal road conditions, especially in the northern US includes numerous potholes. If that becomes an excuse then they might as well just deny transmission work in the hills, and radiator fixes in the desert, and fuel injector malfunctions in the frigid winter. I had a smiliar issue with my GTO and the dealer eventually ended up replacing two rims becuase they stated that for the warranty to be void I would have had to have hit a pot hole large enough to have dragged the car and they couldn't find any drag marks on the bottom of the vehicle. They did however try for about a month to deny the claim, I just stuck to my guns and eventually they gave in.