Clyde Hathaway I have an old manual That calls out the 303 this oil has been discontinued because it was made of a compound that included Sperm Whale oil. I also have a manual that is apparently newer than the one calling out 303 and it calls out 90W oil. SO I just used a multi wt gear oil. I don’t see where it would mix with the tractor or transmission hydraulic system. I prefer the heaver lubricants on the chain and sprocket or gear system that are enclosed from the dust element. The stuff that is out side the hydraulic or light weight oils applied more often help keep the dust and dirt from accumulating. Phil P