I have 2006 model JTDm with similar (now) mileage you are looking at. I would recommend you check the following:
1) Clutch bite and when test driving do the revs rise and then drop before rising normally when you put your foot down in 3rd/4th/5th or 6th - any strange feeling in the clutch probably means you're gonna have to change it - look out for heavy clutch pedal/notchy clutch pedal;
2) 2006, 06 plate onwards are fitted with "swirl flaps" - check the rod on the inlet manifold by removing the engine cover (plenty of threads). probably a big ask to ask to remove the engine cover, I know - but worth the hassle otherwise it can be a pricey fix cos you may as well change the belt and waterpump whilst the thing is off!
3) check roof and around windscreen for bubbling paint/poorly fitting seals.
4) Is engine a bit hesitant under around 2k rpm - if so, it's EGR and easy enough fix easy DIY and LOADS of threads and how to's.
5) are any of the digital displays flashing/do they fade when you start up - battery or proxy alignment issue - easy enough fix but needs diagnostic equipment.
6) Blackline = trim level - black paintwork, nice alloys (bought some for mine!), dash is a slightly darker silver and black leather (diesels) or black cloth (1.8ts) with red trim.
7) check windows drop when you open the doors and just make sure you give it a damned good looking over - otherwise, a great motor with plenty of space and very sexy!