Always had this problem with iron heads due to the thin valve cover rail. If I have the heads off I dissasemble them and run a flat file over the rails, they are very porous and must let the oil seep through, but since ive started filing them flat and smooth I have no leaks! Even with the old cork gaskets
The magnums are machined. Us poor LA guys have to file +Dremel away. I should have taken pics , the casting porosity makes me wonder how any LA valve covers sealed.
