Of course I went and re-looked at the cap on my 2016. It has no large washer or O-ring, just the big rubber gasket with a nut holding it in place. So mine is 5 years old with 7k miles, and the gasket is firm and appears to have no visible signs of wear. To those who have modified, are you simply placing a large washer over the gasket (leaving the perimeter free to seal the rim of the filler opening) and using the same nut, with some Loc-Tite type product?
