The rubber seal that insulates the fuel filler neck
from the underbody where you put the gas in has been a long requested reproduction part and we're glad to have them available. Take a look at yours - probably dried up, cracked and ugly looking. These new seals also come with new installation hardware for a great finishing touch. You may also want to take a look at the condition of the fuel filler neck
itself; if it's rusty inside OR out, consider replacing it at the same time.