The O-ring(1wg) is the cheapest item from this partsfiche.
Parts such as the Repair Kit 1: O-ring (688), Gasket (663) (nas), Oil Seal (6h3), Gasket, Cylinder Head 1 (nas) are included in the P60thv 1997 Repair Kit 1 parts fiche.
The Yamaha REPAIR KIT 1 has thirty products enlisted in the schematic.