Recently had to pull motor for overhaul at 277,000. Passenger motor mount needs replaced, half came out with motor and half stayed in truck. Is it the single bolt on the face of the mount or the nut that is "locked in"? The head of the bolt on both mounts are rounded off, and looks like I will not be able to get an extractor on them, and I can't get nut to break loose no matter how much heat and or penetrant I use, impact just sits there hammering on the nut.