Is there a mileage that the tdv8 turbo's fail around or is it just down to luck?

(I've searched but can't find an answer)

Good question but I don't think there is a definitive answer.

No doubt there will be the odd rogue turbo that fails prematurely because it has a manufacturing fault. Mostly though it is poor maintenance or bad driving habits that are most likely to account for failure.

Most of what can be said about causes of failure and what can be done to avoid it has been said here:
http://www.rrsport.co.uk/forum/topic32013.html

Other things to watch out for are absolute cleanliness when changing the air filter - even tiny bits of leaf litter, pine cones etc. left in filter housing can be sucked in to the turbo blades and cause terminal damage. Leaky hoses could allow dust and dirt to be drawn in too. 2008 MY Java Black TDV8 HSE