I put a TC DIY up a while back that should help. The X-drive TC takes slightly less than one liter and I bought genuine BMW X-drive fluid at ECS Tuning - $50 for one liter. When you see the fluid coming out you will be glad you swapped it.

As for the diffs, I did those for the first time at 80k and I have to say the fluid looked absolutely brand new. I was shocked. They could have easily gone to 100k on my X. I did the tranmission fluid at 100k and it looked great too but still not as good as the diffs. Again, I was surprised.