One end of that tube goes into the top of the front differential.

The other end attaches (around those two radial rib things a few inches before the u-turn) to a bracket near the top of the engine oil dipstick tube. I expect if you forget about the vent tube for a moment and look at your dipstick tube you will see some clues that make it clear.

I have the same car as you - 2001 3.0i, same color too, and that's how mine is.

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2001 X5 3.0i, 203k miles, AT, owned since 2014