Over 11 years of very harsh treatment there have been quite a few, some caused by previous abuse. Only once has it failed to finish a journey.
Most serious: head gasket failure around 80,000 miles, caused by repeated overheating/refilling on a trip to Hungary (caused by broken fan cowling vibrating against and holing radiator, and being in a tearing hurry so we just had to press on). Ignored resulting water leak which meant a complete strip-down and engine rebuild at 100,000 miles (GBP 1000). Been totally reliable for another 80,000 miles.
Camshaft oil seal (~40,000).
Injection pump driveshaft seal (~60,000).
Clutch actuator lever bent (~90,000m) - the one time I had to get breakdown recovery on a journey. Welded straight in 20 minutes and still in use!
Clutch cable snapped (170,000m).
Clutch pedal weld failed (pedal bent off to one side!) (110,000m).
Accelerator cable snapped (50,000m).
Fan sensor electric connection unreliable (leading to overheating) (90,000m) - needed a good clean.
Significant rust after 12 years old (sills, inside bulkhead, inner wings, footwells, behind rear lights) - rear wheel arch seam bad after 5 years.
Rear suspension bushes/bearings prone to failure after about 130000m - not DIY-able, cheapest to get a new rear axle from the scrappy.
Glow plug failed every 40,000m or so.
Persistent starter solenoid problem - won't turn over when hot. Wire direct from battery always starts it. Replacement of any of: solenoid/earth strap/battery/starter/ignition switch/starter cable fixes it for a while. Eventually added a second relay to the circuit which did the trick.
Headlight switch failed (130,000m).
Low fuel warning light/sensor failed (60,000m) - never bothered to fix that.
Brake disc sheared off when parking (48,000m) - must have been faulty manufacture, but they wouldn't admit it.
Lower suspension arm loose in wheel bearing carrier (60,000m).
Windscreen wiper motor failure (50,000m).
Door catches (on body) sheared off (110,000m) - poor design lets them rust out in a neat circle.
Driver's seatbelt tends not to unreel (150,000m)