Technical Leaking gas cap woes

So, I have been cruising the Produce truck on a daily basis. One of the bugs I have, is my brand new Bob Drake fuel cap, it leaks like a sieve.

It was flopping around, so I built a gasket. Whatever I built it out of, isn’t impervious to gasoline and it’s falling apart. I need to find a substance, like rubber to fab a gasket. What is gasoline resistant? Is neoprene? I thought maybe leather? Oh yeah, it’s a factory tank and the factory vented neck.

Tired of it spilling in the rear fender and plus my mileage may go up.

 

good luck trying to get a Drakes cap to seal

 

I used cork gasket material,I bought a roll at NAPA. HRP

 

SO tired of paying premium prices for below average parts.