Actually pretty common, never experienced it but crops up enough for me to be familiar with it already lol!

There are extended drive shafts out for just this reason and a few DIY and documented repairs here and all over the forums.

IIRC it comes about from an AC evaporator drain that drips right on that area and it rusts out.

A proper fix I think would be to service both the diff and replace the shaft but a lot just use the longer shaft and it seems to work.

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04 X5 3.0i auto
03 X5 4.6is