This Rear Caliper diagram displays the required parts for the Gsxr750 1989 (k) (e01 E02 E15 E16 E17 E18 E21 22 24 25 34 39 53) Rear Caliper.
Some items from this specific schematic: Bolt, Bolt, Boot, Spring.
On this parts fiche the Seal,piston is the most specified component.