The custom billet thermostat housing from Roush allows you to ditch the cheap stock version and uses an integrated O-Ring. There is no need for a gasket on the housing to spacer side. You still need a gasket on the spacer to manifold side. I beleive the o ring is just a round oring formed to the groove of the housing. I think with a touch of heat you can almost preform it in the groove or you could tack it in with a hint of permatex on install. I switched mine to the Roush housing when I replaced my intake gasket. High quality part and no leaks or drips.
