A hevier weight oil just prolongs the inevitable. Frommy understanging, changing a head gasket on the duratec's isn't very difficult at all. The egnienc an stay in the car. Remove the UIM/LIM and your basically there. Takes minimal tools, minimal money, and about a day.
Edit: the dealership wouldn't know it has a salvage title.
I say just get a few bears, a few CEGer's a few tools, and the right gaskets and git-r-done your self. Great way to get "intouch" with the car.
