Tastes aside, a manual 300D Turbo would not be a smooth ride. Its hard enough for the S-class automatic to smooth the car, I don't care if your Mario Adretti, the car will be down right harsh. I am sure Mercedes tried the manual in the 300D back in the day, they didn't offer one for a reason, in fact, they have never offered a turbo charged diesel in a stick, not even in Europe!

Case in point, when the w124 300E came out, they offered a manual. Albeit not a great seller, you can't say they didn't offer the 300D in a stick for it wouldn't be the volume leader. It just didn't work!