Mine is a 3.0i, but I think it's a similar or identical design. But I can see that I might have a lot better access (pretty easy actually, from above) to this joint than on a V8.

I found about 1" rotational "play" in the steering wheel when I first got my x5. I similarly recruited one of my kids to turn the steering wheel side to side while I was feeling down on the u-joint, steering rack area. This allowed me to isolate exactly what was loose, which was not clear until doing this very carefully (I had first thought it was a problem in the steering rack interface, which was wrong).

In my case, the double u-joint assembly itself was fine, but the problem was that the set screw(s?) holding it to the steering shaft were not holding it firmly. So the u-joint had a little play with respect to the steering shaft. I fixed that by loosening the screw(s?), cleaning everything carefully, and reassembling with loctite. A critical part of the tightening was to get it centered before locking it down - so my daughter was wiggling the steering wheel back and forth as I was telling her what amplitude to use, and as it settled into the natural center, I finalized the torquing.

Zero play after that.

And my double-u-joint is still fine after 186k miles, but of course yours might be worn out. The testing I mention above should be able to isolate whether the slop is within the joint itself or in an interface above or below it.

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