The eleven Gsx1100f 1989 (k) Usa (e03) Front Brake Hose component parts are all listed in this schematic.
On this parts fiche the Washer(10x15x1.5) is the most specified component.
The most reasonably priced component used on the Gsx1100f 1989 (k) Usa (e03) Front Brake Hose is the Washer(10x15x1.5).