I did put some sealer on the threads when I added those small gaskets. When I removed the star washers, all four screws had evidence of oil creeping or leaking. Today, it appears that the DS were not leaking and the PS were definitely leaking. Yes, I've added a spin-on oil filter and a PCV valve, but I can't imagine those being the problem. The engine has bypass oiling so a 1/16" reducer is in the outlet side of the oil filter. The PCV valve was installed in a modified draft tube and is an open system. There aren't any vents in the valve cover; however, the oil fill cap is vented.
This gasket has been in place for around three years. Recently, I noticed the oil accumulating in the lip of the valve cover. I do not find any evidence of an oil leak between the gasket and the head. I'll run it again tomorrow. Most likely, the gasket has just failed or I didn't have it sealed very well in the first place.
