Pretty sure you have the six speed ZF 6HP26Z transmission, so it won't likely be water in the trans. connector. In addition, our 3.0D models have a large plastic splash guard, covering the transmission from, well, splashes. :-)

What might be an issue is the rather common trans. fluid leak from the mechatronic seal, resulting on low fluid levels. This can be hard to spot, since the leaking fluid is often trapped in the splash guard - no tell-tale fluid spots under the car.

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