philminotti It depends on which valve cover you are using and which material of gaskets. I started with steel valve covers and double rubber gaskets. They didn't seal well either way. I added spread bars to them and this helped. I glued the rubber gaskets to the heads and smoothed out the transition between heads and intake. A spot of RTV sealer at this point also helped. The problem was doing valve adjustments after 3-4 times the gaskets leaked. They where not crushed or over tightened. I got the nice aluminum Lemans valve covers and went to the 5/16" thick cork gaskets. I Hi-tac them to the Valve covers and have been using the same set for 6 years with 2-3 valve adjustments check a year. I have had no leaks from this setup. IMO this aluminum valve cover spreads the holding force better that a steel cover. Big thing is to no over tighten them. Contact and a 1/8 turn is all I use. Make sure you check your intke gasket for being clear of water ports and
oil returns. I have seen gasket pinch up and get crushed when installing and not following the correct torque pattern. Rick L.