If your X6 has over 80,000, certainly over 100,000 miles, it is time to rebuild the front and rear suspension. Since you just purchased the X5, I guess it would be safe to assume you intend to keep it for awhile. You can see the part prices and the parts needed at Bavauto. Labor hours depend on who will be doing the work. Members in your area can provide you a range. Find the best Indy shop with the best reviews. If you can't afford to both ends at once, I would do the front first.

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