I use Permatex Ultra Copper hi heat gasket sealant. A thin layer on the flange and in the holes. I have also used NordLoc washers under the bolts and that combination is solid. I've heard others use red Loctite but I have not.....Ultra Copper is the best material I've used so far and it seals and locks everything long term. Lost header bolts just don't happen anymore.....

I am really hoping that Hobby services comes through for me this week....