This schematic depicts all components used in the Gs500eu 1993 (p) Germany Australia (e22 E24) Rear Caliper (model P/r/s/t) partslist.
On this parts fiche the Seal,piston is the most specified component.
The most reasonably priced component used on the Gs500eu 1993 (p) Germany Australia (e22 E24) Rear Caliper (model P/r/s/t) is the Bolt.