I like the liquid brush-on Permatex sealer called "super 300". It's not the same as the #3 brush-on liquid. It's almost black in color, and it was developed for use around 115/145 Avgas. I use it on both sides of steel shim head gaskets. Use no sealer at all on no-retorque head gaskets, or on any gasket that's exposed to intake manifold vacuum. I like yellow 3M weatherstrip adhesive for gluing valve cover gaskets to the covers, or anywhere else where it's important for the gasket to stay in place during installation. We called the yellow stuff "gorilla snot" around most of the race tracks where I've been.
RTV is OK, as long as it's not over-used. A thin layer goes a long way. Don't use it anywhere it might get exposed to liquid gasoline, as it swells up to many times its original volume, and gets pretty gummy in the process.
Jerry
