Before deciding that all E70 diffs are at risk of failure, we should try and determine what these failures have in common.

In Ninja's case, the vehicle is a 2007 3.0d. The part number for the diff was changed up in 2009. The new diff is also used in the four cylinder F25 X3, nowhere else. I think it is fair to say that it is smaller and lighter than other E70 diffs, but I don't know the design rating.

The 3.0sd (higher hp), the 35i, the 35d, and the 48 all use different differentials according to the parts book.

For some non-North American models, there was also an optional differential for towing. Same ratios, different part numbers, increased tow rating. That applied to the 2007 3.0d. So, that is another suggestion that the standard 3.0d diff is not as strong as we all might like it to be. For the 3.0d specifically, the optional (towing) diff is the same part number as is used in the 3.0sd and the 35d, among others. For the 4.8i, there is an optional diff for increased towing capacity outside North America as well. Same ratios, so to my simple mind it comes down to strength (duty cycle) and heat management differences.

I would also be interested in whether any of the vehicles with a failed diff had any tuning done, particularly the diesels that are relatively easy to tune. Not to blame the tuning, but to try and determine whether the failure is more likely related to load, or something else.

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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