Dany gets a racing stripe, or how to seal a gas cap?

Well apparently after 54 years the old Cuda gas cap gasket isn't sealing any more.
I know this is kind of an early A thing but this is the first time this car has ever leaked out the cap after a fillup.
What have you all done to correct this?
Does someone make a repop gasket for our original cap?
Anyone had success with the derilin adapter to attach a flip out cap on an early A?
Any thoughts appreciated as we want to correct this BEFORE the paint is repaired!!!20200520_131507.jpg