Do water pump impellers go bad?

I was wondering if water pumps ever go ‘bad’ by the impeller not functioning as well as when new; either through corrosion of the blades or by mechanical separation from the shaft (like spinning on the shaft)?

The reason that I’m asking is my friends’ 300D (1983). The cooling system checks out OK, thermostat is new (and tested) hoses are new, radiator is only 8 months old, belts are snug, header tank cap is holding pressure, proper antifreeze mix, the auxiliary fan is working – so everything seems to be in order. But the car runs at about 87-89 degrees (Celsius, obviously) without A/C on, and at 95+ with the A/C on. This is during driving at air temperatures of 70-85 degrees, and at pretty much all speeds between 30 & 70 MPH, so the ram air effect should eliminate the fan clutch from the equation.

I have researched previous threads, but I can’t find any that seem to be the same problem. This is assuming that it *IS* a problem. In previous threads, it seems as though the 123 cars run a little hotter than the 126 cars with the same engine; at least that’s my impression based on the reports from other people. The only other thing that I can think of is if the gauge is not calibrated accurately.

Any ideas?

Thanks In Advance!