I took the time to try and track down a very minor mystery fuel leak today that is originating somewhere behind the back seat, as the leak is evidenced on the underside of the car, forward of the rear axle and just behind the exhaust resonators. It’s not leaking enough to leave a mark on the driveway, but the underside of the car in this area is coated with WVO.
I wanted to expose the fuel tank to see if maybe there was a leak in it or if fuel was getting by the o-ring on the fuel sending unit when I have the tank full. In preparation I searched the archives and printed off reams of paper including
240D fuel tank removal and cleaning
and
W126 removal of 1st aid kit box
as well as
http://www.diymbrepair.co/Sender/
All of these talked about accessing the fuel sender through the first aid box. Well on my car the fuel sender is accessed from behind the seat back, not through the first aid box. I sure am glad I stumbled across that access point before removing the parcel shelf in order to remove the first aid box.
I never did find the leak even after exposing the entire fuel tank. With the exception of the underside of the car, everything is dry including the fuel lines under the tank. I may be seeing some seepage around the nut of the fuel strainer, but I can’t imagine a bad o-ring there would cause the wide spread mess I’m seeing, and besides, it’s not that messy at that nut.
The day wasn’t a total loss. I changed the oil, put some pool noodles in the back seat (what a huge improvement) and learned a little bit more about the car. Maybe this post about the location of the sender on this model will help out someone as ignorant as myself.
Here's some pictures of the fuel sender access: