Both differentials, and the power steering fluid, are considered lifetime fluids by BMW. There is no downside to changing them, and owners often use either 60,000 or 100,000 as the interval. Make sure you use the correct fluids. You can also change the transfer case fluid at the same interval. It uses a special fluid from BMW.

Automatic transmissions are a different story. Officially they are lifetime fluids. Some people believe in changing them on the chance that that will extend transmission life. Others don't believe in changing transmission fluid on this vehicle, even though they change all the other fluids on the vehicle. I am in that club. There is a potential of a fluid change precipitating a transmission failure. Not common, but frequent enough to be a risk. At the same time, there is no evidence that changing transmission fluid prolongs the life of these transmissions. Both the ZF and GM transmissions used in BMW X5 models have failed more often than we would like to see, but those failures don't appear to be related to worn fluid. They do appear to be related to various sensors, actuators, etc. So it is either change it on the hope that that helps, or save your money for when (and if) you do need a transmission overhaul on the assumption that it is just throwing money away. Your call. Do some reading on the board and you will find lots of discussion, it tends to generate strong opinions.

Jeff

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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