Hylomar spray is the only sealer I will use on Cometics!
I remove the rivets that hold the layers together, clean the various layers with dish soap and hot water (washing them by hand), Dry and apply the sealer to every other surface. Every mating gasket/head/deck surface has Hylomar on it . I realize that the guys at Cometic would object to any sealer or my cleaning process, but I am not asking them !! It works for me. I have many high output engines (including my own) running where I have used this process.
Just remember, even the best sealed head will have a problem if detonation occurs. If the gasket stays sealed, detonation will break the next weakest part!
DR