I just bought a used 2002 525iT wagon. The xenon headlight assembly is broke, in that the parts inside the plastic housing slop around freely - bulbs are OK. So I obviously need a replacement and have been searching everywhere. I see a ton of halogen lights that look exactly the as my xenon unit - except for the transformer. The question is whether or not I can use a halogen unit and mount the xenon hardware as a direct replacement.
Your problem is broken headlight adjusters It's a very common problem, and lets your lights bounce all over the place. Very distracting at night. In the e39 models through 2000, the headlight adjusters were available from BMW dealers as replacement parts. I guess BMW decided the 2001+ assemblies were robust enough that the adjusters would never need replacement, but they still break at nearly the same rate. There are no fixes from BMW, but there is an aftermarket source for the adjusters. I think somebody was so fed up with the plastic adjusters that they had a large set of metal adjusters manufactured. I'm sure a search on the roadfly e39 board will help you find the source. I've got 2 1999 e39s, so I have not actually had to use the aftermarket parts myself.