Here is my problem. I have a stainless steel Rock Valley 15 gallon gas tank in my 1934 Ford Coupe. It has an aluminum gas cap with an "O" ring inside. The tank is an older unit with a bottom feed. The gas cap fits a two and a half inch neck. It has worn out, and it has fine thread. Upon calling Rock Valley I was told that they no longer make units with fine thread caps ,and that the cap I need is no longer available. Has anyone got a cap . Any info appreciated.