I have a friend in my club that has a tool... a machined plug that fits perfectly into the inner dome of head and glow plug hole. If the plug seal is deformed... it will not seat completely on the bottom of dome and rocks.... good seal... seats perfect and will not rock. Amazingly simple. I don't know where you get one of these other than your local machinist friend (I suspect it came from one of two of our local machinist/racers).