Good suggestions, all! If the gasket is fairly flexible, I'd install it "as is". If it's dried out and brittle, a good soak in hot water, with a little dab of RTV rubber sealer on both sides might be a good idea. Don't overdo it on the RTV, a little goes a long way, and you don't want any excess falling into the gas tank.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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