if you are on warranty then its dealer, otherwise you can order it yourself it would come out much cheaper (getbmwparts.com) and either install it yourself or have any mechanic do it. (plug in connector and sealant tape around the fixture)

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2007 4.8i X5 - Monaco Blue/Beige
Sport - Tech - Cold Weather - Rear Entertainment - 3rd Row Seats - Premium Sound - Rear Climate