I'd just buy a rubber one at the hardware store if the trip to the LHBS is out of the way. It won't hurt for a few days so you can tune in the kegerator and try it out. They may even have a silicone or neoprene washer there. I never looked.
Day after day, it reappears. Night after night my heartbeat shows the fear. Ghosts appear and fade away. Come back another day.