Hello,
I have to conclude that w/p life really is just a *luck of the draw* kind of thing. All my cars have always run the genuine manufacturer recommended coolant. The newer Mercedes with the automatic tensioner multi-vee belts have an advantage in the sense that the belt cannot be overtensioned. My observation has been that the M103/104 and later V-6/V-8s have long pump life, up to 160K+miles.
Have a good weekend.

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Nachi11744