Maybe, you'll find the answer here. You can thank Prof Mclare by gifting him an apple, or maybe a beer 
http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1446652-c126-w126-water-pump-r-r.html
http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1446652-c126-w126-water-pump-r-r.html