It is amazing to me that these German car manufacturers keep pushing plastic bits for pumps and pressure parts in the cooling systems. This same problem exists in the BMW community, but thank goodness one manufacturer now makes all metal replacement pumps and radiators for BMW's. Surely someone must do the same for the M96 engines, or do they just expect the IMS to crap out first?

Theres been lots of opinions regarding metal impellars. Both Jake Raby and John (JFP in PA) recommend the original plastic because if the W/P bearings wear or even collapse, the metal impellers will grind through the alloy crankcase quick smart.... Goodbye engine.
At least with the plastic composite impeller blades, they can break or wear off (just like Spinnakers) and not cause immediate damage.
So Raby may be correct in recommending W/P changeout every 4-5 years. At ~$250 a pump + 3 hours of my time, its cheap isurance.....