I have a 2003 E55 and whenever I'd fill up and drive a while, I'd have a strong odor of fuel outside of the car. I suspected that this had something to do with the fuel pump under the rear bench, but I never smelled much of anything inside of the car. Only outside...particularly near the passenger side rear. Further, I'd intermittently get the "replace fuel cap" red error on the dash with a check engine light and code P0455. But, I just installed a new cap a month ago.

While searching for the solution to the gas cap error, I stumbled upon this video from a guy with the exact same issue.

This isn't me in the video, but searching the web lead me to that video and solution (including part numbers near the end):
When I removed the fender liner, I smelled the smell. And when I removed the old filter, I smelled it even more. As in the video, my filtering element was black and seemingly clogged (not as porous as it should be). I think the filter was just full after over 18 years of service.

I followed the instructions in the video and it works. And just like him, I had issues getting the new filter in place. I fought that sumb*tch for a full hour. Seriously. It would NOT go in. I realized that the new o-ring was gripping tightly when I attempted to press and turn to lock the filter in place. So, I sprayed glass cleaner on my fingers then rubbed it on the o-ring to provide some temporary lubrication for the turn as it locked in place. This worked immediately!

The updated filter, o-ring, and conversion wiring harness (to mate with the updated filter) were $300 at 2 local dealerships. If I ordered from MBUSA parts, it would have been under $200, but I would have had to wait until next week to receive them (even with pickup at the dealership). The dealerships will match MBUSA pricing, but apparently that has to be approved by the Internet Parts Manager who wasn't in until Monday. So, I paid $100 extra because this weekend was the only time I have to do such in the next few weeks. Totally worth it as it would have been much more at the dealership or even an independent. Beginning to end should be maybe 20 minutes for a mechanic, less than an hour for weekend mechanics like myself. Fighting that o-ring made it close to 2 hrs for me.

 

Dam... I had a filter sitting on the shelf. Wish I knew I could have helped you out.
Yea that filter housing man....how did your thumbs feel after that LOL !!!

 

That would have helped a lot. I didn't like paying full retail for the part, but I wanted to knock it out that day.

Yeah, my fingers were crying after the install. Using the glass cleaner helped A LOT. Like first try after rubbing some on the o-ring. That tip will save the next guy/lady lots of pain.