My recently sold 1972 Prevost is still mostly original.
On the engine the only thing replaced- beside belts and couple houses was fan clutch.
The air-operated clutch simply corroded in unprotected coach.
So quality parts will last 50 years and even my coach had low mileage, the drive-train was 1 million miles rated.
Bad news is that I notice degradation in automotive parts.
My father still owns 29 years old Mercedes, where plastic parts still hold.
Our 8 years old model has plastic parts chalking.
Come to the point where when I need replacement plastic grommet for 8 years old car, I go on junk yard and pull the same part in good condition from 25 y/o model.