Some items from this specific schematic: Pump Assy.,oil, Bolt,flange,6x22, O-ring,11x2.5x4, Dowel,pin,8x14.
The lowest price component in this E-12 Oil Pump parts-list fiche is the Bolt,flange,6x22.
With a quantity of two pieces, the O-ring,14.6x3.6 is the most used part in the E-12 OIL PUMP diagram.