Floor pan is part of the body. Maybe not a structural part of the unibody but still a part you left out that drastically affects the car's value.
Hidden floor pan rust won't be the only issue. You see, that rubberized coating is everywhere which is why the only REAL way to check for rust is with a screwdriver, poking at all areas to see if it goes through. The rubberized coating cracks, lets moisture in, and the unibody rusts sight unseen until the rubberized coating falls off to reveal holes. Ask us how we know!!
IMO the diesel Benzes are only worthwhile if they run well and are rust-free. They use more expensive fuel than a gasser and modern gassers with way more power will get better MPG, so only a few diehards would want a rusty example and they will not pay much for it. I'd suggest selling it. You MIGHT get $1000 if you're lucky and can get it to start and run around the block.