I just bought one from the link in RG's post (above). Had 3 in stock. I paid $15.45 (now listed at $16.50). Two-day delivery with Amazon Prime. VERY EASY to install ... just remove the filler cap, pull out the old gasket and slip on the new one ... about 15 seconds of work (add another 30 seconds to clean the area before installing the new gasket) ... nothing to disassemble. So easy that it isn't worth making a tutorial.
1. old dry brittle and torn fuel door gasket
2. new rubber gasket installed (filler cap removed). New rubber makes the contact area much quieter when the fuel door closes.