The fifteen Gsf1200 1998 (w) (e02 E04 E18 E22 E25 E34) / P37 Rear Caliper (gsf1200t/v/w/x/st/sv/sw/sx) component parts are all listed in this schematic.
On this parts fiche the Bolt,housing is the most specified component.
The Rear Caliper (gsf1200t/v/w/x/st/sv/sw/sx) assembly is constructed from several parts from which the Caliper Assembly,rear is the most expensive.