I had a similar problem with our X5 a month ago..initially I suspected it was the transmission leaked but turned out to be a faulty PCV valve which caused abnormally high internal pressures forcing oil past gaskets and seals.

hope this helps.

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'07 X5 3.0d - Black Sapphire Metallic / Camel interior
Specs: Sport pack, Executive, 7 Seats, OEM 336, Hifi
Mods: Aero Kits, Titanium grilles, 4.8i exhaust, Tinted, ///M Footrest, OEM Sport pedals, OEM Rubber mats, OEM Sunshades, LCI Taillights