2V help needed

Gas will get in over time (years) through tiny pinholes where the seam is soldered. Changes in barometric pressure and altitude will "suck" the fuel in. It won't come back out because the holes are so small that air can't get back in to displace the fuel. Think of how a tire loses pressure over time. You can dunk it in water and never see a bubble but after 6 months or year, the air does seep out very, very slowly.