The component with the lowest price in the CYLINDER schematic is the O-ring(36y).
Check out any of the four Cylinder components enlisted.
Parts such as the Cylinder: Bolt, Socket, Gasket, Cylinder (nas), O-ring(36y), Cylinder 1 are included in the Xg250 2005 4d62 Austria 1d4d6-351f1 Cylinder parts fiche.