Razor thin layer of copper RTV works well and provides some color to the engine as well. However, any sensor safe RTV sealant should work. It was not equipped with a gasket.
i've tryed all different types of sealant and it still leaks. i'm tired of taking it off and cleaning it up all the time. i think im going to try and make a gasket, is there any good reason why i shouldnt use a gasket?