This heat-riser valve has a large buildup of scale and corrosion on theflat sealing surface. Using a gasket will stop an exhaust leak for awhile, but as the fiber seal wears, the gasket becomes loose and theleaks begin. If you're using a gasket be sure to specify it for theexhaust heat riser. Some gaskets do not have the metal ring that keepsthe hot exhaust gases off the fiber gasket material. Replacementheat-riser valves are available and reasonably priced.