Differentials (and the transfer case) have both a drain and a fill. If you are doing them yourself, loosen the fill before draining.

The differentials use 75w-90 (from memory - check yourself). They are not limited slip differentials, and thus don't need LSD additives or special oil.

The dealer will do your transfer case fluid change, it is a straightforward job.

None of these compartments have the risks that are associated with transmission fluid changes, they are simple drain and fill procedures.

How many miles do you have on it? Seems early for a change.

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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