I have a 1990 toyota celica that has a gas leak. the gas comes out of the top where u put gas in the car or out of the over flow. You can see it coming out of the car and can smell it . I try only to put about 1/2 tank in but, sometimes I forget and would like to fix this. Tried a new cap, the gas tank looks in good condition no rust. do you have any idea why this would happen?