I think I have a blown head gasket due to water filing out one of my sparkplugs. I can tell that water is getting on the plug when I take it out because it is showing rust like water from the radiator. My question is. If I use K+W block sealer is it possible for this to stop my plug from filing out? Will it stop the leak. Im not losing any power except when the car is idling so I don't think the leak is very big. I just put new plugs in the car and the same one filed out twice after I ran it for a little while. Please help.

Stay away from sealers and get the job done properly, if the car is worth keeping. Sealers can permanently interfere with fixing the problem.