I just today finished replacing the belt, tensioner, fan bearing and an idler on a M103. I considered replacing the water pump because I was "already in there." Easily another half day doing the water pump from that point so I'm going to wait untilt it has to be done... hopefully not next week.
From the perspective of having to do it myself, $560 is a bargain. From the perspective of just about any other car on the road, $560 for a water pump is not that bad. Most FWD Japanese cars have water pumps that are more complicated to replace than that of a M103. *However*, my opinion and experience is that Japanese car water pumps don't need replacing as frequently as MB water pumps seem to require.
Maybe German submarine engineers should quit desinging MB water pumps.