Hi 100k is fine they are good engines and as said before as long as the service history is good then go for it. The engine is actually gear driven crank to cam so no issue with belts etc.There are a couple of pointers.
1 the diesel particulate filter DPF service life is around 120k depending on how it’s been driven it’s around £1800 to get it replaced and never go non genuine they cause all sorts of issues.
2 the one and only big issue with these engines was the exhaust manifold studs breaking on cylinder one, look for exhaust gas around the brake servo area and signs of soot.
3 The gasket between the turbo and engine block had a habit of leaking take a good look underneath to make sure there are no signs of oil loss. Not a big job to replace just a pain.
I’m not in any way trying to put you of buying this vehicle they are great vehicles and you will enjoy meany happy miles I know of one vehicle with that engine that’s just clocked over 800k