sorry for not replying sooner but had to dig a little to find what i had seen before.
From what i have seen they aren't able to commison customer bearings for the crank

High milage is 100k+ from the posts i recall.
http://www.disco3.co.uk/forum/topic55170.html
Its possible the extra standard weight is killing it off as even pulling off from the lights extra grunt is being pushed through the units compared to a C6/5 or Jag with the same unit. they will also have more drag just in normal running as well as the disco's are fulltime 4x4...
The post above seems to indicate its a well known issue so i think its maybe a design flaw but it does worry me a little for future purchasers and for our beloved double chevron'd vehicles could fail at a higher milage.
Maybe also playing into the fact is that C6's are not as 'stressed' on a regular basis compared to an LR vehicle which does need a good welly to get it to shift sometimes... just look at my avg mpg over 1600 miles in over a week, 25.6....