Are you sure the gas is coming out the vent hole? My cap was leaking, but it was from below the seal. The tank was dented at one time, so the top of the fuel opening wasn't flat, plus there were a couple of small dents that would let fuel out when the tank built up a little pressure. I took a small piece of broken glass and laid it on the opening. It rocked around so I could tell it wasn't flat. I bent it from underneath until it was as flat as I could get it. Then I sanded it flat with a sanding disc. It still seeps a little, but nothing like it was before. At least now it doesn't run down the side of the tank. A crotch fire would not be fun.