Do you remove your own rear wheel for tire changes?
If so, you have enough skill to consider this:
http://www.valkyrieriders.com/shoptalk/5204_bearing_mod.pdfOr, just replace the existing bearing, which is what I did. Might do the Mod when mine fails or next tire change (just put a new tire on, bearings felt fine). I've seen the axle spacers on Ebay for ridiculous $, but entire rear axles WITH the nut and spacer for the same or less $.
Collar, Rear Axle, 42313-422-000 is used on multiple model Hondas.
https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2499337.m570.l1313&_nkw=42313-422-000&_sacat=0Good luck if you do need a mechanic. Can't help you "there".