Parts such as the Oil Pump: Screw,cross 5x10, Cover,oil Pump, Gasket,oil Pump (nas), Screw,cross 6x16 are included in the Z50j2 Monkey 1989 (k) Finland Rot Oil Pump parts fiche.
The Screw,cross 5x10 is the cheapest item from this partsfiche.
With three applications this Screw-washer,5x10 is the most specified part.