I replace my water pump two weeks ago on my 2006 X5 M54 engine with 108,000 miles. To my surprise my engine water pump was metal or a composite material similar to metal, not the plastic compound that is mention all over the forum. I was kind of upset because it is recommended to replace all the cooling system parts at 90,000, I waited 18,000 more and still no sign on ageing on any part replace parts.