Damn... 540K miles? There are very few diesel trucks that logged that many miles.
I wonder how many clutches he had to replace? And bearings?
I imagine the engine is still original (i.e. un-opened), but does it lowers some oil? What was his oil change interval?
I don't think he has had any clutch or engine work done. He did have a run of bad luck with pinion flanges and driveshafts. But I think it was fixed with a new swing arm. His was clogged on the weep holes it was found out. He recently posted about his oil changes. I think he does them at about 5k.