On this parts fiche the O Ring 2031 is the most specified component.
A sample from the products for the 010 Half Crankcases include: Ball Bearing 6003 Tn9 C3, Right Bracket, Screw Tcei M8x75, Nut.
The lowest price component in this 010 Half Crankcases parts-list fiche is the Gasket, Aluminium 12x16x1.5.