Super glue works to make custom O rings from bulk stock. I've made dozens of them when repairing hydraulic equipment. If you can find some flat seal material instead of round, it might be worth a try.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!