I have a 6.5 H.P Briggs on a Generac Pressure washer. It developed a leak on the OHV cover. I have replaced the gasket two times, Tried using gasket sealant and not using gasket sealant. Cleaned mating surfaces very well. No matter what I do after I shut the unit down I get a small pool of oil coming from the bottom of the Valve cover. Any advice would be appreciated. This should be simple, but it is kickin' my Arse !!!