For those that have done a water pump on an M103
 

Did you need to replace the metal "drain" pipe as well? All the parts sites say I MAY need to.

The one that runs down towards the crank pulley? Nah, i wouldn't worry about it.

No unless it's damaged.

what metal drain pipe? I've done my water pump twice, so obviously I didn't change it, just curious as to what it is and where its located?

The metal pipe that runs along the block and attaches to the waterpump housing.

Digging deep into the cobwebs of my brain....
 

When I changed out the water pump on my 87 300E ten years ago, I recall this question.

I *think* the explanation was that the water pump had changed at some point, and if you had the early one, you needed this part to adapt the later style.

Jim

This is what I am gathering as true. I will keep it in mind. Thanks, all.

This is true. I would replace it, it's cheap, and the new part will look much better, even though you never see it :)

This is correct. Look at your current one, then compare to the new pump, it should be obvious.
It does have an O-Ring you should get regardless. Along with the pump-> head pipe coolant hose.