Man, if you have to pull the Head to apply some Sealant ... you'd be better off ... in the long run ... to put a brand new gasket on there. You KNOW the old ones bad. Gasket treatments and sealants are made to reinforce GOOD Gaskets.

I never heard of anyone knowing the had a bad gasket just popping the head and spreading around some treatment. You got the Head OFF anyway ... why not put a brand new gasket on there and not have to worry about it on the future.

Since you did overheat it ... you need to straight-edge the mating surface of the Head anyway to check that it didn't warp.