ok, my car is about to hit 60k miles soon so I want to change out the
waterpump. The thermostat and drive belts were changed at 53k miles.

I have heard about the infamous plastic impeller on the water pumps
and to avoid aftermarket pumps (Graf and Geba) but to go with BMW OE
water pump, not OEM...

ok, so what is the difference between OE and OEM, besides the one
letter??? :-)

where do I find the BMW OE water pump, besides the dealer? do some
waterpumps come with the composite impeller??  where can I find this?
I searched Bavauto, Pelicaparts, Autohausaz, and mileoneparts, but
either they have the BMW waterpump with the plastic or metal impeller,
or they have the aftermarket Grab/Graf pumps...