If the oil is some how getting to the threads and migrating up the threads and thru the gasket, then just coat the threads with high tack, or something. Adding a fiber washer would not stop it if that is what is happening. If that is what is happening, you need to seal the thread. Jerry said locktite way back in the post. I lean away from needing locked and toward needing sealed. Locktite may seal but I don't like it on those particular screws.
There is not much pressure in there. If there is, maybe you created a problem with some recent PCV action you took? Does the cover have any "openings"? If so what type? Was any "opening" recently changed? I did read about the spin on filter..............But not super clear on what all that was.
I don't know what's so bad about over oiling a motor and I don't think 5 lbs extra oil pressure is a big deal. I now am forced to lean towards a non flat cover or bad gasket.
I've never seen oil migrate up the threads of a valve cover.
I would like to know if it is both sides, and how many "screws" are leaking.
