It's been a while but I ran a fleet of ambulances with most being diesel (older 7.3 and a few 6.9).
We changed the oil every 5,000 and never had any problems.
One unit had 100,000 miles on it after one year of use.
I do not remember any of the 35 units that needed oil between changes.
They were a couple of the older gas engines that needed much oil but they were 460 with 220,000 miles on them.