[Gelbster]

Important to find all the broken parts of the impeller. If you don't you can be sure they are obstructing coolant flow.When I rebuilt my M96 I found impeller bits in the oil/coolant cooler that probably rendered it useless and certainly restricted flow. Who knows where else in this huge cooling system the plastic bits might lodge. The cost of the potential damage is eye watering. So routine replacement before failure as others recommend is wise advice.
DOn't forget to buy the correct O rings for the cooler !