When the gas pump stops - don't add anymore gas. In my '95 E420, if too much gas is put in it wreaks of gas smell. Dealer told me there was an overflow valve, and that's where the gas smell was coming from.

I used to get in about another 1/2 galloon or so after the pump first shut off. Stopped topping it off and the smell went away. Right or wrong, it worked. Try not topping off gas next time and see what happens.