I may have misunderstood you.....and posted my engine oil change intervals in post #99 above.
I’m still shooting for 30k drain and fills and 60k sump filter changes on the ol’ AS69RC.....although I miss them on occasion.
Yea I was going g WTF???
I would think since you put about as good of mileage on a rig as possible you could extend those changes by double with no ill effects.
I would do an analysis just for fun to see how the fluid is doing at 30k.