Replacing the water pump usually requires that you remove the radiator so you will have room to access the pump body bolted to the head and block.

I haven't done this on my SL, so I cant give details. Haines manuals are available from places like AutoZone, etc, and give a detailed how-to.

Yes, it sounds like a water pump leaking. Only other possibility may be hoses, or head gaskets! .......BB