Sorry for the delay's. I had foregotten what I did with the file I kept with the part numbers. Turns out it was on my old old laptop. Anyways, part numbers:
Plug (nut): 90301-SR3-000 *Note, I had these backwards, fixed now
Bolt (optional): 90156-SH3-000
I honestly would recommend not getting their bolt as it's way too long and you'll end up having to use a fat stack of washers to make it work. Just get the plug which I think is ~$15 and take it to a hard ware store and find a suitable bolt. I believe it's a 6mm bolt. You'll use the stock rubber seal that goes around the wiper arm. Then get two washers so that when you tighten the bolt it puts pressure on the rubber seal
When dissassembling the area around the rear wiper there are some externally visable clips with a small circle in the center of them. If you press this little center in it will release the clip without breaking it.