That's exactly what happened! I must have been shopping for my R53 MINI and didn't set it back to the Classic Mini. Anyway, the cost between getting the new rubber material and fabricating another gasket wasn't too much less than a new gas cap. Order placed last week. Crickets so far. We'll see if/when this is actually delivered.

Depends if you've chosen Classic vs. modern BINI (fooled me the first time as well)  It does not, as default, search both MINI's (which is backwards to my mind, but whatever)

Classic Mini Gas Cap Seal

Those are all for classic minis. 

Thanks again, Willy_B, I did the search before I posted my question here. Those are all for BINIs, not Classic Minis, I believe. Hard to believe Mini Mania doesn't have a gas cap for the Classics. 

https://www.minimania.com/Search_Results/petrol%20cap/Parts

If you are searching on a UK site look for petrol cap. 

Thanks, Willy_B. I run this car on the track and can't afford to risk any gas leakage in the corners, otherwise I would do exactly what you recommend. There has to be a plug and play replacement out there somewhere!

If can remove your old gasket and use it as a pattern then you can buy a small sheet of rubber and make a new seal. https://www.mcmaster.com/8957N11/

Looking to replace my gas cap, which is leaking gas on corners due to a cracked gasket. The only ones I saw on the site were for the modern MINI. Thanks for the help in advance. ??