Water pump removal on your 103 motor has been discussed many times here. Some believe you need a special $50 tool from Snap-On. Others have done it w/o the tool.

I would say if your auto repair experience is limited to oil changes, etc., this task might best be left to someone else.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"