Hi, I am new to the BMW world as I had traded my mustang cobra in for an e39. I absolutely love the car, best decision I ever made. However I am reading on the forums that the cooling system is a known problem. My car has 71k on it right now, I believe the major weakness is the water pump which has a plastic impeller instead of a metal one. My question for you is should I just change the water pump or do I really need to change the entire cooling system. That seems a bit extreme, and hard to believe since BMW makes such a high quality product. Thank you for your advice.