I have the cap. There must be a way to make a simple gasket for it. How do I know if I buy a used one on eBay that gasket is any better than the one on mine? Aren't the used ones 40 + years old maybe?
If it was me, I would go to my favorite parts store and buy a roll of cork gasket. My roll is made by victor.
Cut a new gasket. It doesn't have to be perfect. Use something like a antifreeze lid for a pattern or whatever is close to what you need.
