Sorry, but on most MB vehicles the headlight washer hoses run across the vehicle at the front bumper. You may have to have the bumper cover removed inspect it. Many times the headlight washer nozzle breaks or becomes disconnected from the hose and the siphoning affect drains the washer system. To see if the sprayer is working or disconnected, you should turn the ignition on and have somebody actuate the headlight washer as you stand in front of the vehicle, if the left headlight sprayer comes forward and sprays, you should compare the spray pattern against that of the right side. If the left side does not spray, but there is a large leak behind the left headlight, then you probably have a hose disconnected. You may have to have the vehicle raised on a hoist to see the source of your problem. Good luck.