1.Those valve covers are notorious for leaking. sme of the allen bolts that came with mine were actually to long. they looked OK but were actually bottoming out before supplying sufficent pressure on the gasket! I had to grind about 1/8" of the ends for them to seat properly.
2. The gaskets are imporatnt. I tried the Felpro with the metal in them, I forget what they,re called and I tried cork. Both worked for a while and started leaking.
3. RC specs different gaskets for each type of cover and showed me what he does. For those it's felpro VS50156R. You then glue the gaskets on the valve cover with RTV, Put the valve cover on a perfectly flat surface. He uses a starrett granite lapping stone but glass would work, put a heavy weight on the valve covers and leave for a couple of days for the RTV to completely cure. Install the valve covers. Not a hint of a leak in 3 years. I bout a couple of sets because I don't think they make them anymore but plenty are still available on line.