On this parts fiche the Washer Seal 8mm is the most specified component.
Parts such as the E-2: Case,thermost, Bolt,stud Special, Nut,hex.cap, Head Comp,cyln. are included in the Cn250 Fusion 1993 (p) Japan Mf02-140 E-2 parts fiche.
The E-2 assembly is constructed from several parts from which the Head Comp,cyln. is the most expensive.