Nothing like the Bentley manual that I am aware of, but there may be something.

Look up the factory TIS if you like.

Here is the page for the transfer case oil change.

BMW TIS - 00 11 572 Changing oil in transfer box (ATC 400/500)

Whole thing here:

BMW TIS Online • 3' E83

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue