I bought a set of cast aluminum adapters from a hot rod shop in Sun Valley about 40 years ago. Even with the best molded silicone gaskets they leaked. The Cobra Lemans covers looked great on my SBC, but no matter what I did, there was always a small dribble from the lower edge on both sides. I have reinstalled them from time to time, but always have the same issue. If it was a show car, I would probably put up with it. But, as a rally car that gets driven lots of miles, I cannot stand it.
I have recently given thought that maybe the problem is porosity through the aluminum. If I painted the 3 edges (that do not show) with some kind of
oil resistant paint, that might stop the leak. However, I have a great set of cast aluminum chrome covers that look great and never leak, so I am not very motivated to change them. I just run Ford Performance breathers and a distributor-less ignition system, so no one realizes what engine it is until I ask them to figure it out. When they look at the exhaust headers they get it. It's a fun game at a car show.
RS