One of the "Display Defective" messages means the coolant level sensor-washer fluid level sensor circuit is open (too high of a resistance). That is how Mercedes programmed it. It is not a defective display but rather a bad choice of words for the error message.

Since you have already replaced the coolant level sensor, now measure the resistance of the washer fluid level sensor. Just unplug the connector and use a multimeter to measure (with a full reservoir). It should be around 170 ohms. If it is much higher than that, replace the washer fluid level sensor.

http://www.benzworld.org/forums/w210-e-class/1298824-display-defective-error-message.html#post3468758