Yes turf it is quite common on this era diesel engines to have these road-draft vent tubes which will expell more and more oil as the engine wears and piston/ring clearances get greater. Cylinder walls get glazed too, so compression pressure gets past the rings into the crankcase, soňo, that pressure, has to go somewhere and as this flow increases it carries more and more vapor and droplets with it.
For those of you who are not familiar with these engines and may only have experience with passenger vehicles, you may or may not know that this blow-by is handled in a different way. Since the late 50's early 60's this 8blow-by is re-circulated and drawn back into the intake manifold to be re-burned. So although your grocery-getter may have just as much blow-by (or maybe even more if it's a high-miler) as your, new-to-you, bus, you wont see it cause it's getting sucked-in & re-burned. Older (pre-sixties) cars and light trucks all used to have these open, road-draft crankcase vents and they were always marking-their-territory with varying sized drops (depending on their age/milage) of oil.
Hope this helps to relieve some of the mystery for you.
P.S. One drop of oil splattered all over your under-carriage always looks like a Lot more.