The O-ring,15.3x3.5 is the cheapest item from this partsfiche.
Parts such as the Oil Pump - Primary Drive Gear: Spring,disk, Pump Assy.,oil, Gear,prim.sub(35t, Collar,o Ring are included in the Cx500t Turbo 1982 (c) Netherlands Oil Pump - Primary Drive Gear parts fiche.
The twenty-three Cx500t Turbo 1982 (c) Netherlands Oil Pump - Primary Drive Gear component parts are all listed in this schematic.