The O Ring(d:2,id:24.5) is the lowest priced item on this Rear Swinging Arm schematic.
Parts such as the Rear Swinging Arm: Torque Link,rear, Spacer,rr Swgarm Pivot, Washer, Bolt(6x8) are included in the Ts100 1978 (c) Usa (e03) Rear Swinging Arm parts fiche.
The most expensive part in this assembly is the Absorber Assembly,rear Shock.