Glad to hear you found the root cause by being diligent.
blykins is right , Someone using two gaskets is a sign from the engine gods! Find and fix the root cause of the deck height to cylinder head intake flange mis match, and have the parts machined correctly. This is a dynamic joint and over time using the two gaskets stacked like you describe will cause a problem again as move in normal hot/cold cycles. It will be a high maintenance joint and will require more frequent tightening. If you must, find or make a custom thicker single gasket, but stacking 2 gaskets is risky and a temp. measure only. I could see this as a quick fix between rounds at the track but not for a street driven car. If it was my engine I'd take it back to the "professional" builder and make him stir his daily coffee with those doubled up gaskets so he remembers.
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Buts thats just me since engines cost so much.
Yes the blue Hylomar is good stuff, racer supply houses carry it, I did same thing as snakebit .... I used the Permatex RIGHT STUFF sealer on the ends of the intake manifold and saved the cork end pieces for the wine!
