Oil is a bit like religion, a matter of faith....
For the records, a friend of mine owns a long-range trucking company with ca. 50 Volvo trucks.
All Diesel as is standard in Europe.
Each of these trucks does around 100.000 km per year.
And he never, ever changes the oil.
The filters yes, very frequently (they are in high position like on our cars).
But for what regards oil, his drivers and mechanics are instructed to just top it up.
And they do like this for more than 10 years without any issue.

 

You just need to reset the service required light. To do that with the engine off and foot off the brake hold the fog light button and the start button at the same time. Then in less than 3 seconds release your finger from the start button and press the button on the end of the directional shaft. Then hold until it resets, about 10 seconds. There is a video on youtube.