Leaky valve cover follow up.

RustyRatRod said

Tell that to my slant 6. They all have machined valve cover rails. I honestly believe the valve cover would have sealed better without a gasket at all. lol

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I kind of meant that with a sturdy valve cover like the mp cast aluminum... unless you have a valve cover like that then I don't know what but can say & recommend the cometic rubber coated fiber it is a great sealing gasket, I had my valve covers off and on many times while Dyno testing.
The other thing with the big blocks factory head is the bolt hole bosses on the lower 4 I believe are at a slight angle and with a slippery gasket can easily not seal since there's only a little bit is pinched between the valve cover and head.