I'm confused on this part description also.. are you describing some rubber cover, that is "over" the rear axle nut, on the right side of the bike?, That part does not exist on any US model ever produced, and was likely "if as I described it" someone's "add on".. not needed.(and may actually hold water in there, to rust stuff up..)... just lightly grease the threads, and the nut, wipe off any excess grease, and insert the cotter key, and lock it..