Well they need to buy at the lower end of the scale so went to look at a TD6 with 135k miles on the clock, to be fair to it the car had been serviced and the interior was in quite good condition, only drove it around for a few minutes but the gears seemed to change ok and it engaged low range ok, couple of points though, it warns that it needs brake pads when it doesn't as they've been done but the handbrake light wouldn't go out, one of the doors feels like there's no tension in the handle and won't open,I think the final stage resistor has gone as the rear fan is working and the front ones the lights came on but no air, I had this problem on mine so knew it straight away, it's also going to need 2 tryes.

Plus points are it has a longish MOT, it's a Vogue,going to go for a second look tomorrow(annoying as I'm looking for a second car at the moment too).

My thoughts are that at 135k if there was going to be gearbox failure it would have happened by now?, so it's either a good one or it's had a replacement already?
The air suspension was a bit slow to change settings but it did go up and down, the car had been sitting for a while,obviously a few marks etc as it's 8 years old but nothing major.
Is this worth a punt at the right money?, or avoid.

Depends what you class as 'right money'

Around the £9k mark.