It's basically a Perkins Prima from what I understand of things and pretty bombproof with good routine maintenance. Cambelt changes are fairly expensive and you have to take the fuel pump off to change 1 glow plug but, that aside, no major issues AFAIK. It's no powerhouse as standard, but relatively easy to squeeze 25-30% more HP and torque out of.
If you do buy it, I've found that Millers Diesel Power 4 makes a big, big improvement to the way it runs.