Most likely the washer pump is not functioning. Turn the key on but don't start the engine, press the washer stalk in and listed for the motor. If the motor is working, then you might have clogged jets. If the motor isn't working, order a new one from your local MB dealer. They're about $25 each, get a new rubber seal with it as well.
Precision Motorcars, Cincinnati, Ohio
'67 250SE Cabriolet
'93 300E 2.8