Fuel Filter connection
Like JH said in the previous post, it could be the fuel filter. I had the same smell on my 300E and could find no leak that was visable. I removed the plastic cover that protects the fuel pump and filter and found a small amount of fuel seeping past the seal. With slight force to the threaded filter nut it stopped and hasn't returned since. Filter and pump are located on the right rear in front of the tire under a plastic shield. Four plastics nuts will have to be removed from the cover to access the pump and filter.
"Tell me and I will listen, Teach me and I will learn, Show me and I will accomplish, Involve me and I will succeed."
'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan