Friction Modifiers, Extreme Pressure additives, and Anti-Wear additives are all friction modifiers to one extent or another, but anti-wear additive films do not provide protection under long-lasting or sustained pressures, due to attrition. However, they will quickly reform providing enough additive reserve was included. So at times the delineation between AW and EP additives is not always clear and somewhat arbitrary. EP films, under extreme pressure, stay intact at higher temperatures and form/reform these films rather quickly after the pressure has passed. Most EP films also form at room temperature, unlike engine oil AW or FM additives. So we can say that the major differences between AW and EP films are that EP films:
a.) Form/reform more quickly
b.) Act or get to the base metal at room temperature, i.e., does not require
elevated pressures/temperatures to start the film reaction (the exception is the phosphate esters)
c.) Act as anti-galling, anti-welding additives
d.) Act/react when the pressures or loads are above what the AW additives can handle.
e.) AW additives form plastic films which "glide," whereas EP additives form films which shear or "slide"
As far as the 20w hydraulic oil, that's too thin for these older primitive hydraulic systems that use steel piston rings on the lift cylinder and no rings on the hydraulic pump pistons. Multiply that times 50 years worth of wear and tear on the pump and a thinner oil will cause more leakage and decreased performance of the lift. That would be like taking an engine that has 100,000 miles on it that was designed for 10w30 and suddenly start running 5w20 in it. You could do it but the engine wouldn't like it and you would have less oil pressure than before. Now in my newer tractors that have more modern hydraulic systems I use modern hydraulic oils.