So guessing you have the 4.4l N62 V8....

You might want to sort the leak before replacing the alternator... or it will just happen again.

Power steering fluid or oil?

As for which alternator..? Entering your VIN into RealOEM and checking the part numbers etc. can help but ultimately, you'll need to match what is installed. It's possible the variations have different connectors etc.

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Wayne
2005 BMW X5 3.0d (b 02/05)
2001 BMW F650GS Dakar (b 06/01)