I might be missing something here but isn't it just missing a metal dust cap like the one next to it....and does that maybe mean that whoever lost the dust cap previously also lost the correct size nut because looking at your pic the nuts are different sizes and that implies to me that someone just bodged that one on after losing everything???.I used 2 of those metal dust cap thingies that I had left over from my 600 as a mod on my gen 2 for my handlebar risers.
I see what your talking about noggythenog, and yet again still none the wiser as hard to tell what's missing as I've never done the job lolBtw, you still got the heated grips? Yes I got involved reading your on going work lol
Oh well there goes my sale of said cap I was wrong......as usual