Just one other thought mate........I'm not sure how long the DPF on the 159's lasts. On my BMW E60 which had about 75k on the clock, the computer was showing as it being due for renewal in about another 25k miles.
It may not be an issue if you do low miles, but I have heard that DPF's (on the Beemers at least), are about £1,500 when due for renewal. It maybe that you can disable them, and then not worry about changing them.
You may want to find out from some of the more technically able forum members here.
There's another thread doing the rounds at the moment "Mileage on a 159? How high so far?". A couple of owners have fairly high milers; might be worth PM to them for their thoughts re the DPF lifespan?