Parts such as the E-4: Screw,tappet Adj., Cotter,valve, Valve,exhaust (jdm), Nut, Tappet. are included in the Md90 1999 (x) Japan Md90-230 E-4 parts fiche.
The most reasonably priced component used on the Md90 1999 (x) Japan Md90-230 E-4 is the Nut, Tappet..
With four applications this Cotter,valve is the most specified part.