The roads while I grew up were awful compared to today's roads and vehicles with more than 100,000 miles seemed to always be worn out. It's very common today to see vehicles with over 200 - 300,000 miles with the original engine.
I remember certain people always making claims about this or that engine oil. "This oil will sludge up everything, this oil never leaves any sludge". I never knew who to believe. I used "piston ease" " recycled" oil in an old oil burner I had.
Interesting there's as much science behind oil as there is.
Oh, why do people call it motor oil??