Worty, you are right nitrile and petrol these days dont mix, the petrol eats into and swells the rubber then the rubber effectively melts away, anything that touches petrol now needs to be viton (seals) or flouro lined tubing.
Unleaded fuel was bad and now ethanol added, its even worse for fuel systems...
Now I'm asking the question, will the nitrile part of the nitrile bonded cork deteriorate? The sheet was sold as fuel and oil resistent.
Worty, I cant tell you if the product you have is any good or not for gaskets, I would think that it would be fine in that situation, but dont know. What I do know from my Ford eng'g days, was that when ULP was introduced we had to upgrade all our fuel lines and gaskets that were in contact with petrol, then upgrade more when Ethanol fuels were introduced - viton was the only solution for O rings used in taps and valves though....
Also, what I do know from personal experience with ethanol fuel inadvertantly used on my (chinese made, Honda copy) generator, is that it expanded the seals in the fuel tap and locked them closed. I had to remove the fuel tank and pipes and clear the ethanol fuel, then replace the tap and lines, all good since
NB it does say in the handbook NOT to use ethanol fuels, when I read it to see what could have happened