The right valve cover on my 1967 Cadillac DeVille always had a small leak and eventually some oil would seep down on the exhaust manifold and cause some smoke when it burnt.
The gasket was replaced a couple of times since I own the car, but it never was very successful in stoping the leakage.
After my last attempt it leaked even more than before…

The valve cover design of the 429 engine is not exactly the best from a technical standpoint. It's only held in place by 4 screws.

I did some research and tried a different approach this time to seal it.

First I used a different valve cover from a spare engine I have in my garage which did not show any signs of leakage.
I had to fully detail it first to make it look perfect. I repainted it with Bill Hirsch Engine enamel in the correct color.
I made sure that everything was flat as these cover often get warped at the bolt holes by over tightening them.
They checked out flat. I then glued the new cork gasket (I used a Fel-Pro gasket) to the valve cover with high temp gasket sealer. To make sure that it stayed where it belongs to I used a lot of cloth pins to keep the gasket in place.
I let it dry over night.
The next day I put some wheel bearing grease to the other side of the gasket and put it back on the heads. The grease helps to make sure that you can remove the gasket any time again.

I then tightened the four bolts to 28 INCH/Pounds of torque as specified by the shop manual. (thats 3,1 NM) I had to buy a small torque wrench for such a small torque rating first… I could have never guessed how much torque it is.

I then ran the engine and let it cool down and re-torqued the bolts afterwards.

After the first 25 miles test drive it seems that the valve cover is 100% leak free for the first time since I own this car.
I´m not sure what fixed it this time, but during my research I read multiple times, that for cork gaskets one should not use gasket sealer on the head side of the gasket, and one should only use grease instead. Some recommend that gasket adhesive (spray) should be used to keep the gasket in place in the valve cover.

I know it looks very strange, but I used cloth pins to make sure that the gasket is glued to the valve cover properly…