Changed fluid on my transfer case this week-end (hit 40,000miles and I'm trying to stick with the "old school preventative maintenance program"). Was much simpler than I first thought (took just under 1hr).
Some tips:
make yourself a 25mm long 14mm hex stubby just like the DIY guide entitled "Transfer Case Fluid - 328xi early 2007" on e9Opost.c0m
this makes all the difference as you don't have to remove the cross brace
I used a GearWrench 85914 XL 14mm GearBox Ratcheting Wrench ordered on Amazon and it worked very well with the stubby hex bit

Next challenge is resetting the adaptations for the clutch inside the transfer case. I'll update this thread when I've figured out how to do that...