Parts such as the Oil Pump: Ball-steel,3/8, Circlip-type-c,11mm, O Ring,16mm, Gasket,oil Pump Cover (nas) are included in the Z550g7 Gt550 1991 Europe Uk Sd Sp Oil Pump parts fiche.
The Oil Pump is made up of components including this Pump-assy-oil which is the most expensive.
The lowest price component in this Oil Pump parts-list fiche is the Circlip-type-c,11mm.