The Washer,6.1x12x1 is the cheapest item from this partsfiche.
A sample from the products for the Oil Pump ('74-'75) include: Spacer,8.3x13x1.0, Oil Seal-oil Pump Sht, Oil Pump Assy, Lever,oil Pump Cable.
The Kawasaki OIL PUMP ('74-'75) has twenty-five products enlisted in the schematic.