[quote="X5Sport"]
If you haven't already got a decent after market warranty then give serious consideration to getting one! When these cars break, they break expensively.
The gearbox has to be your primary area of concern, as you have latched onto, but read the various threads before you do anything. Whilst many owners have no problems after a gearbox service other get a failed unit very soon afterwards. There is nothing to say which it will be.
If you have a ZF gearbox specialist nearby then go and talk to them as they should be able to tell you all the pluses and minuses that come with these beasts.
Check all of the electrics work, have look down by the battery (under the spare wheel in the boot) for any signs of water - and to get the age of the battery whilst you are at it.
If you have an hour or so to kill, take the car into a BMW Dealer or Bosch Autologic Agent and get all the fault logs read both for 'present' meaning it's there now, and 'not present' meaning has occurred in the past, errors. It might identify anything of concern that you need to look at - or give you a clean bill if health.

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Brilliant advice, thank you.
Do you recommend any warranty companies? and what would you recommend to set the claim limit to? £1000? £2000? I don't know how much the most expensive repair would be so would need an idea.
It's going for a winter check at my local BMW indy towards the end of the week so I'll ask them to check the codes etc.