Don't most auto makers suggest replacing timing belts at around 70k miles. And I also seem to recall that every mechanic I've ever had replace one also recommended replacing the water pump while replacing the timing belt.

I don't think 120k miles is an unreasonable life cycle on a part that does what a water pump does.

I would imagine that you could also attribute a shorter water pump life to belts that are too tight. It would put undue stress on the seals in the pump and cause them to wear out faster.

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'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.