[AKnowles]

Actually, black flakes do not have to be the water pump vanes. Or at least my water pump vanes were fine and from what I could tell of the black flakes were actually rubber and assumed to be part of the water hoses. Water hoses will deteriorate and it is not abnormal to see the flakes in the flushed coolant/water. I replaced my aft hoses when I replaced the water pump and will replace the fore water hoses this fall when I add the center radiator.

Now, if he is seeing a LOT of particles and not flakes like your picture it might well be the water pump vanes.