I have a 1999 F250 (V10) with 103,000 miles on it. The spark plug in #4 cylinder has come out of the head and the threads are damaged. Has anyone heard of this happening or does anyone have any theories on how this could happen? All 10 plugs were replaced around 68,000 miles by the dealership where I bought the truck. The servicemen at the dealership have never seen anything like this and think that the plug had to have been blown out or that something got into the combustion chamber that knocked the plug out. I don't see how this could happen and the top of the piston (viewed with a bore scope) doesn't appear to be damaged. Any help would be appreciated considering my options are to pull the head and try to repair or replace at around $4000 or put in a remanufatured motor at around $5500.