I just tried Seal All to mount a couple duckbills in the gas cap. Thanks for that. I think the Seal All held but the duckbills started leaking after a couple of tanks of gas. Maybe I should not mount the duckbills directly in the cap as someone else suggested installing a pen housing to extend outward to remotely mount the duckbill. Thios think is kicking my butt and I have quite a collection of ruined gas caps.