Unfortunately there's no such thing as a little oil leak on an X5, especially a V8 engine...lol! Look inside your stiffener plate, that's the silver plate bolted underneath the engine, it's probably full of oil and road sand. The plate will actually catch and hold the oil over time preventing it from dripping on the ground, hope I'm wrong though.

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2002 X5 4.6is
1999 C5 Corvette
1992 Mitsubishi 3000GT VR-4
1994 Kawasaki ZX-9R
2005 Mazda 6 Wagon (Wife's)
1991 Mitsubishi 3000GT VR-4