I have the single exhaust head pipe that has the four bolt flange where the CAT bolts up. I have no CAT but I am using a cheater pipe with that same four bolt flange on the end. I have the correct thick aluminum gasket. The head pipe flange is in pretty bad shape. I wanted to use some kind of sealer to make sure there is no exhaust leak at the flange. What will seal well but not go bad from water or other abuse?