So I finally get my collector plates, and I have to take my 75 Dart Swinger in for it's last emissions test ever. Part of the Wisconsin emissions test is checking the gas cap. When I showed up at the emissions test, my cap had a good vacuum seal. By the time I left, the gas cap was just hanging from the car!

The gas cap still locks onto the car, but it no longer creates a vacuum seal over the fill tube. It looks like whatever the pimply teenage emissions tech did, he ruined the foam ring that was on the cap. Is there a way to get a replacement for this piece of foam that made the vacuum work in the first place? Any templates out there that I can use to make my own foam ring? Do I need to start trolling eBay for a "new" gas cap?

Help from anyone else who has been down this road already would be appreciated!

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'75 Dart Swinger, bone stock 225, 1 bbl carb