A sample from the products for the E-8 include: Screw,flat.4x12, Roter,oil Pump, O-ring,9.4x2.4, Gasket,oil.pomp (nas).
On this parts fiche the O-ring,9.4x2.4 is the most specified component.
The most reasonably priced component used on the Xz100 Ape 2002 (2) Japan Hc07-100 E-8 is the Screw,flat.4x12.