In a rig that old, it could have been leaking for a very long time. It's not a question if there's dry rot, but only how extensive it is in both the ceiling and the floor. Unless your there when they open it up, I would never accept their word on any repair. They'll patch it up and say your good to go, but you will find out differently later. Myself, I would demand a full refund or else. It doesn't matter how big the dealership is or how many lawyers they have. All that matters is you YOU ARE RIGHT and you will win. Sometimes all it takes is a phone call from an attorney to set them straight. Roof leaks are the hidden demon lurking inside some old RV's that will suck the money out of you like a tornado. Good luck I wish you a happy outcome.