My '64 Ford 2000 4 cyl gas engine gas valve located under the gas tank leaks. Its a screw driver slotted multi-turn helical thread shut off valve that seems to be leaking thru the valve "thread", even when its fully screwed in the off position. The original one leaked so I replaced it and now the "new" one is leaking. Its a pain in the butt because the tank won't hold any gas overnight. Has another else had this problem? Does anyone have a solution?