At 85,000 miles I would do a complete rebuild. Old parts can decrease the life of new parts if you go piece by piece. Major BMW parts sources have kits. Though cost is higher I suggest the OEM kit though some offer all BMW parts and a lower price point with various MFGs

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas