The rervoir is located behind the bumper, below the headlamp housing, passenger side. The MB suggested way is to remove the bumper, and possibly the headlamp housing. I guess evidently the bumper is held by only four bolts two of which are the hood bumpers, and two more behind the access panels on bumper. The sides of the bumper are in slides.
There are the sender, pump, heated tubes from the radiator, and on earlier mdels a hose to the plastic indicator tube. Mine is stuck on full, I just have not gotten around to it.