I have used Blue Hylomar on head gaskets since 1979. Never had a head gasket leak during this time. I use it on all paper gaskets and they never leak either. Petrol unions,oil drain plug, in fact, any surface that has to keep oil petrol or water in the right place. I have used copper permatex on some outer covers but it is a silicone type. It will seal if the two surfaces have no gasket.
Having used blue Hylomar this long and getting no oil or petrol leaks, it is my preferred product. Back in the 60s, we were using red and golden hermetite. Often, this was to seal parts we had wrecked by prising things with chisels before we could buy some proper tools. This was the reason old British bikes got that bad oil leak reputation. Us young ones using bicycle tools and old WW2 hammers.
Having used blue Hylomar this long and getting no oil or petrol leaks, it is my preferred product. Back in the 60s, we were using red and golden hermetite. Often, this was to seal parts we had wrecked by prising things with chisels before we could buy some proper tools. This was the reason old British bikes got that bad oil leak reputation. Us young ones using bicycle tools and old WW2 hammers.