2008 Impala, 3.5 engine. After returning home, I added gas to the Impala's tank, and noticed that the gas cap has a rubber gasket that appears worn, which could be a possible cause of the occasional P0455 code. The gasket goes against the filler tube. A quick online search didn't return anything about the gasket alone. Is it possible to just replace the gasket, and if so, where would I find one aftermarket? Napa, O'Reilly and CarQuest are in this town, and Advance, AutoZone and A-Line are about 25 miles away.