Most AWD BMWs seem to share the same arrangement as far as front driveshaft/diff/TC are concerned. That means they also share the same problems.

Concerning the driveshaft splines stripping in the TC hub, like it has been said, the fact that the spines don't engage very far into the TC doesn't help since the load is spread only on a small part of the splines.

That problem is also present on the E30 325ix.
I did something to my ix that I think could be applied to the X5 to help the driveshaft spines live longer, or give few extra miles to a damaged one (assuming the the TC hub is still good).

I fabricated a 1/2" spacer to fit between the front diff flange and the driveshaft. With that spacer installed, almost all of the driveshaft splines are inserted inside the TC hub.
The holes in the driveshaft need to be threaded, and studs made. That solution seems to work well. My E30 is turbocharged, and the splines are still thight.

Here are a couple of pictures:

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