[quote=""smeeagain""]Undoubtedly the 'randomness' of gearbox failure is linked to maintenance and driving style/conditions (eg town driving with lots of gear changes v motorway cruising)
Most folks don't maintain their car as much as think they do, or as much as they should, nor drive as well as they think they do. [/quote]
I disagree with this statement as it's a bit too sweeping. Linking the 'randomness' to driving style is I feel a little tenuous at best. If it wasn't then BMW would not do any goodwill replacements at all, and a fair number of owners have had BMW stump up for all or a large proportion of the bill. BMW GB refused mine as they said I had Warranty Direct Cover. The Dealer said it would be goodwill, but then told BMW GB about the WD cover and they walked away. Mine was BMW maintained throughout on a service plan and the gearbox destroyed itself at less than 5 years and less than 42,000 miles. These boxes are 'Sealed for Life' so there is no maintenance plan at that mileage. I have a normal driving pattern of mixed roads etc, normal driving style, never abused, raced or rallied etc. A cheap plastic part in the TC broke and by sheer bad luck and jammed the oil pump. Pressure failed and the rest is expensive history!! The repairer had 5 more BMWs with the same box (5's and 7's) and also other vehicles with the same transmission (Jaguar & LandRover) all awaiting rebuilds for either clutch failures or TC failures resulting in other consequential damage. What he did say is that the 'Sealed for Life' does not mean what you think it might. It is for the 'useful life of the vehicle' - which may well be 6 years or less if the comments of my BMW Dealer are anything to go by, and is probably why they will not offer OEM warranties of more than three years from new without additional expense to the Owner. If these cars are made from such rock solid, high quality components and were once the 'Ultimate Driving Machine' then they should come with a warranty commensurate with that don't you think?
There is a 'known weakness' of this transmission which has been accepted in the US but not in the UK (mainly down to weak rules about what constitutes such a defect and getting the manufacturer to foot the bill as a result). That being said, I have friends with auto's on their cars which are not ZF unit and have had failures too, some very early and again not connected with maintenance or driving style either. And again I have known of cars with auto's that have gone on for years and never given any issues up to the point the car met the scrappy's shredder But in all likelihood, the actual number of failures compared to the number of cars produced is still very low - people would not buy auto's otherwise.
There will be far more X5's which have never had any issues than there are with failures in the gearbox. As you say, we only ever read about the bad ones and not the good. And the odds are probably hundreds to one in favour of no problems. But here's a thought - ZF introduced a modified version of this box we have and the number of failures have dropped off if what I've seen reported in the various forums is anything to go by.. Might be something in it, or nothing at all. There are some pretty high mileage E70s about now though.
I would agree though that turbo failures are more
likely with driving style, especially if the warm up cool down measures aren't adopted. There's nothing like shutting off a car with a red hot turbo and so cooking the oil to start a premature bearing failure.
better economy and performance
Still making me smile every time I drive it and after nearly a year that's saying something and I've owned a lot of cars 
Never anthropomorphise computers. They hate that.