As far as water pumps for a 103 engine go, the dealer item with the STAR is the best. I paid $100 about 2 yrs. ago for one. I would not use a reman. While you have the pump off, also change the short hose(1.5"-2.0" long) that runs between the T-stat housing and the cyl. head. This is an opportune time to replace this bugger. The MB part # for this hose is 103-203-00-82.
The other hoses are easy to replace. Their age and condition will determine if replacement is necessary.
As far as how to do a 103 water pump goes, look through the archives. Much has been written on this subject. The MB CD-Rom is VERY useful here too. Unless you're BencMac, there is alot that has to come off in order to do a 103 water pump.
1991 300-SEL - Model 126
M103 - SOHC
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