[rotorwrench]

Motor oil has evolved in order to protect the catalytic converters in modern cars so they lowered the amount of high pressure additive otherwise known as ZDDP. It has had corrosion preventatives and additives to hold particles in suspension for many years. The ZDDP wasn't in high concentrations until valve trains were beefed up for high compression, high torque, and high horsepower ratings in the 50s. The cams & tappets had a lot more pressure on them than the old flatheads did. The advent of adding polymer plastics was probably the largest evolution so that they could have multi viscosity lubricants that would work year round.