I put plugs in my X headed 408 and the one plug I had to use a breaker bar to remove. See pic., The other 7 were all fine so I guess I have a cracked head in this cylinder. I didn't notice any water in the oil or excess water out of the exhaust though the coolant level was down. I ran a compression test and it was ok for now but I would assume if I continue to run it its just a matter of time before that changes. My question is has anyone ever successfully fixed a cracked head or is it time for a replacement?