On this parts fiche the Cushion is the most specified component.
seven components are shown in this Gsxr750 2004 (k4) Usa (e03) Seat Tail Box (gsx-r750k5) exploded diagram.
The Seat Tail Box (gsx-r750k5) assembly is constructed from several parts from which the Box Assy,seat Tail(blue) is the most expensive.