Umm, I do believe they ARE responsible for the damage since the radiator is supposed to cool the water that cools the engine, it didn't work! It seems most likely that the radiator wasn't properly cooling the engine and the engine got so hot the oil had no where to go but out. I've actually seen this before when a friend of mine had similar problems and the oil cap actually blew off the engine. (No, it wasn't the radiator cap, it was the oil cap. Although that cap went missing as well!) I think you can make a pretty strong case to suggest it was most likely their fault. Just take it up with Judge Judy!