Ridge, a diesel engine can last a long time, I doubt any will make it to 8-10k hours without some repair or rebuild even with strict maintenance.
The ones rebuilt before 2,000 hours are probably neglected, abused and have been overheated at some point. I have 800 hours on mine with nothing needing repaired/replaced but a shifter spring, I do change the oil /filter at 50 hours, fuel filter every spring, new air filter every other spring, hydraulic fluid every 300 hours, I know the manual states the intervals to be longer but I think its cheap insurance to keep the fluids fresh.