I have that transmission in my 01 X5 (E53). I've changed fluid and filter twice; once at about 80k and again at about 155k. I use Valvoline MaxLife Dex/Merc. Still shifts like the day I bought it (I bought it new). I'm at 161k miles.
Be sure to clean the pan, especially any fine debris around the magnets in the pan. Resist the urge to clean the valve body; you don't want any lint in there.
12 BMW X5 3.5i xDrive (E70)
12 Audi A4 Quattro 2.0 turbo (the black sheep)
03 BMW 330i ZHP (E46)
01 BMW X5 3.0i (E53)
79 Triumph Spitfire
73 MGB