A coolant leak may develop from the water pump. When replacing the water pump, the drive belt tensioner should be inspected and most likely replaced as well.Google+
Car Problem Reports
Mercedes-Benz C280 Check Belt Tensioner When Replacing Water Pump
Mercedes-Benz C280 Problem
Visitor, 1995 Mercedes-Benz C280, 160,000 mi
WATER PUMP WENT OUT. DEALER REPLACED PUMP BUT NOT BELT TENSIONER. LESS THAM 1K MILES LATER REPLACED TENSIONER- ADDN $400.