i run dynatech headers LT's, on the donut gasket spray it with a high temp sealant. i also made a flange gasket that fit around the donut for extra seal... you can get these already cut from an exhaust shop, may have to trim the ID alittle but it solves all issues of leaks, also nuts i use are the flange nuts, they have ribs on them to tighten against the outer flange, keeps from backing off..