Hi Nick, depending on year youre looking at... An early D2 is a 1.6 ford/citroen derived lump, I was previously a massive supporter of this engine, widely used in Mini, Fords, Pugs, Citroens and others across the globe, must be ok... Thats until the 3rd clutch/flywheel assembly replacement lasting 1000 miles, then I decided to pass it on. My wifes C30 was diagnosed as needing an engine, an earlier version of the D2 literally made of chocolate. There are some real horror stories.
The later D2 is Volvo's own 2.0 unit, with dpf and egr issues if you only ever do short journeys, as with any modern diesel. . I chose the 2.0D2 pre April '17 so I can stick two fingers up at gov (zero tax) Hasnt broken down in 18 mths, has had an EGR + cooler (paid by Volvo), never been less than 52 mpg