Might be different in Australia, but in North America recalls are for safety and emissions reasons, not for parts that don't meet owner's life expectations.

As for part numbers being changed up, it can be for any number of reasons, including simply a supplier change. It isn't an indication that there is necessarily a design or manufacturing problem. Do we know what the part number change up signified?

I agree that a differential shouldn't break under normal use. The existence of a stronger diff for certain models, however, suggests that the standard diff may not have had as much safety margin as other models.

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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