Have a 2001 Grand Caravan that was at the shop today (3.8L engine w/82K miles.) The Service Manager indicated they could not do a tune-up due to the fact that one of the plugs on the front bank was seized in the head and he was afraid to strip the head out. Any idea how prevalent a seized plug is in this engine and what the success is of trying to get them out without tearing the threads out of the head?