I had the rocker cover gaskets replaced when I had some rockers replaced. The new Mahle rubber gasket has leaked oil on top the left hand side of the inlet manifold.
The garage have said their supplier told them as the covers are Mickey Thompson aluminum covers on standard heads, it needs a cork gasket not a rubber one. I find this strange as I had no problems with the previous rubber gasket (of unknown make). Any suggestions would be apreciated.
Stephen
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Dear Stephen,
They contend that the combination of aluminum valve covers and cast iron heads dictates a cork valve cover gasket for optimal fitment and to prevent oil leaks?
Hmm. The last three Cleveland engines I built used rubber or silicone valve cover gaskets in the setting of aluminum valve covers and cast iron heads. None of them leak. My advice is to respectfully disregard the supplier's recommendations.
I would suggest surveying the valve cover gasket choices on Summit or JEGS or maybe even TMeyer and pick a rubber or silicone gasket. I seem to recall Mr. Gasket and Victor Reinz have them. I think FelPro may also offer a rubber option.
Warmest regards, Chuck Engles
Dear Chuck
That was my sense. Thanks for confirming it for me.
Thanks
Stephen
Valve cover gaskets are just a general pain to begin with. Don't use them at all. Use silicone instead. It's a much better solution. It isn't subject to uneven compression and cracking like many are.
Cork gaskets are about the worst solution. They don't compress evenly and are not reusable anyway. Just glue the covers down with silicone. You can easily crack the valve cover as a result.
Your shop didn't suggest this to you? 
They should have unless they did and were over ruled by an MBA? 
I recently installed these with success............
help educate me.
I would think a big factor in getting a valve cover to seal would be the proper bolting torque and tightening sequence. I'm thinking it would be very easy to over torque
I've used the rubber and the cork, the latter for the last six or seven years . No leaks.
The 'cork' is really just evenly shredded cork bits bonded in a rubber compound, not much different than the solid rubber version.
Install either type with a light wipe of silicone sealer on the valve cover side of the gasket. No sealer on the engine side and you can easily remove and replace the rocker cover without damaging the gasket. The gasket stays bonded to the rocker cover.
Tighten evenly, not too much, there are eight bolts at work. That's more than most engines. Often a leak is from a cracked flange. Hard to see, gets worse as you keep tightening. The earlier aluminum covers had much thinner flanges than the later ones.
A regular retorqing of all your various engine fasteners helps to stay ahead of the leaks. Every spring my carb bowl screws will take around a quarter turn to re-snug them.
