One trick for water pump longevity is to use the proper MB antifreeze, or Zerex G-05, which is the same thing. It keeps the ph of the antifreeze proper so it does not corrode.

I pulled the pump out of my 87 300SDL when it was overheating, and the pump impellers were badly rusted and the volutes of the aluminum pump cover were also badly corroded. The right antifreeze prevents this.

Gerry