Found this searching the Old Tech Archives;
Posted By: ChrisjCMA CR3M <
chrisj357@cox.net>
Date: 4/2/2008 at 17:45:08
In Response To: GAS CAP (Leon (#1860))
to deal with it is to get some gas resistant gasket material and make a supplemental gasket that will fit in there with the rubber one....as far as I know ou cant just buy a new gasket. I have done this on serveral motorcycle gas tanks and it usually does great, the hardest part is finding the correct thickness gasket to use.
Good luck