Just a thought:
It seems as if you are loosing A LOT of fuel, but the next time you have the car up on a lift, take a look at the fuel pumps. I was getting bad mileage on my 1988 190 E and when I had it up on a lift, I was looking around (making mental notes of what I want to up grade) and poking around (no rust!) and I noticed the little cup/cap/retainer that covers the fuel pumps was moist. The fuel pumps are by the rear axle, drivers (left) side and I think most 190s have two of them - in series, so to speak. When I pulled off the pump cover, it was full of fuel. I detected a crack on one of the fuel lines (the one between the stage one and stage two pump) and replacing that solved a number of problems I was having. I never noticed fuel on the ground. I think that was because the cover held so much. When I drove, it would spill out. When I stopped, and turned the motor off, there was no more leaking. That's why I never saw a puddle of fuel on the driveway. Anyway, it's just a thought, but you might look into it.