The brake fluid reservoir cap and the fuel cap on the white GTE I have at the shop both needed new gaskets. The fuel cap pictured on the right had a rubber gasket that has shrunk and hardened through the years. Rubber will eventually harden with age, but I believe the varying cocktail of alcohol and additives in fuel can speed up this aging process, so I replaced these gaskets with cork. I have found fuel safe cork gasket material found at the auto parts store to work best for these gaskets, and it’s ironic a natural material is more resistant to modern chemicals than any synthetic material!
I first break up and dig the old rubber material out of the fuel cap and then hand cut a replacement gasket to slide under the lip of the cap. Both caps are now ready for service.