We have had the best luck with copper gaskets,O ringed block with receiver grooves in the heads.for us the cometic didn't work as well.
I assume you have water in the heads,if so install a shrader valve in the cooling system,get a 26 lb cap and pump the pressure up to 26 lbs with air it will help keep bubbles from forming on the back of the combustion chamber walls and that will help prevent detonation which is causing your leakage. Ceramic coating the combustion chambers helps a lot as well. Bill