Sealing compression is a lot easier than sealing coolant. Most composite head gaskets have a built-in coolant sealer on both sides, so adding brush on or spray on sealer is a "belt and suspenders" approach- - - -nice, but probably not necessary. Back when I was using .023" thick steel shim head gaskets to minimize piston-to-head clearance on the zero deck height race engines we built, brush-on Permatex Super 300 was my preferred sealer.
The MOPAR hemi tractor pull engines we built had no head gasket at all- - - -just a copper O ring in a groove around the cylinder machined into the block and brush-on sealer. Of course, the cooling passages were filled with epoxy, and we only ran coolant in the aluminum heads.
Jerry
