It's not a "hidden" warranty at all.
Owners were notified by letter when the owner notification took place. I used to have the letter on my desk before I moved last year. Since I'm well over 100K, I tossed it instead of packing it.
It is the flapper valve located on the very end (outlet) of the filler pipe where the fuel dumps into the tank.
The gasket listed is the one that seals the filler tube mates with the tank.
Steve