Hi usually when you hit the accelerator to overtake, it's common to have black smoke coming out of the exhaust ..
I have the 3.0 CRD also from Mercedes and I have the same , it's unburned fuel
Probably you have a small air leak in the fresh air system.. I've seen it on some 2.7..
Don't worry if it's when it's only during sudden accelerations
I've already seen brand new cars with a puff of black smoke behind them when they overtake
I've heard that once when you use these kind of cleaners ,after that you need to use them quite often .. but I never used them