Parts such as the Front Fork (gs400n:f.no.71032~,gs400en:f.no.504510~): Nut (8mm), Tube,fork,left,outer, Spacer,front Fork Spring, Stud 8x25 are included in the Gs400e 1978 (c) (e01 E02 E04 E17 E18 E21 E22 E24 E25 E30 E34 E39 Front Fork (gs400n:f.no.71032~,gs400en:f.no.504510~) parts fiche.
On this parts fiche the Spacer,oil Seal is the most specified component.