On my '95 E420 had a gas smell problem when I first got the car. Took it to the dealer and they asked if I topped off the gas when filling the tank. Yet bet! They responded, don't do that.

So, stopped doing it and the gas problem went away. Evidently there is an overflow valve (or something to that effect) towards the front of the car. I was putting in too much gas, hence the smell.

Now, when I fill up the car, when the nozzle shuts off the first time I don't add anymore gas. Something could be wrong, but this solution has worked for 2 years.