The Washer,6mm is the cheapest item from this partsfiche.
Some items from this specific schematic: O-ring,9.0x1.7, O,ring.3,ox35, Gasket,r C/case (mca), O-ring,100x2.6.
eighteen components are shown in this Ch125 Spacy 1986 (g) England Gasket Kit B exploded diagram.