If you still haven't found it, try this - had this happen on mine;
Lift the back seat bench on the drivers side and lift up the centre flap of carpet under there, you'll see a black plastoc cover screwed in with 3 screws, unscrew it and you'll see the top of the tank, it has a plastic collar that may just need tightening (like a big bottle cap).
Mine was loose and was spilling petrol all over the place and it stunk in the car and outside the car because it ran down the outside of the tank.