I just did a transmission fluid service, and while I was at it I did the front bevel gear fluid (or whatever BMW calls it).
Car has 25K on it, and the fluid looked terrible. I've had several other Haldex-equipped cars, and the front bevel box fluid always seems to take a beating (unlike the rear differential). I think it's a lot worse on the BMW, since the sump is so small. VW and Volvo both have about twice the fluid capacity vs. the 500ml sump on the X1.
Drain and fill is really easy, since there's a fill and drain plug. I'd really recommend changing this fluid.
Since I plan on changing this fluid pretty regularly (every 20K or so) and I'm always looking for an excuse to buy a new tool, this would really come in handy to get the air scoop out of the way:
https://www.mscdirect.com/product/details/85380715
There are two E8 bolts, one of which is a bit of a pain to get to with a 3/8 drive socket... Was wishing I had something like this when doing the change.