Well this one's exciting guys. Anyways, two years ago when I bought my C5 it had no boot for the main positive connection on the alternator. Kindof bothers me and looks unfinished.
I searched many times for a part number on the internet and forums and never found anything. Literally nothing. Nothing used on eBay, part number, aftermarket ones that work, etc.
So even the best diagrams I could find online, were still bad compared to the diagrams at the dealership.
I went there to pick up some copper banjo bolt washers, and honestly didn't think they would have an answer on the alt boot.
He did finally get a part number but wasn't able to get it at all because of the stuff lately.
So i got a part number!

12146808

Mouser had it apparently and was listed as a boot. I'm a big fan of them so ordered it.
JUST in case this was maybe the wrong part number or something, I ordered an aftermarket one off eBay as well that claimed to work.

So here are some pics below. From me looking at the alternator, the first thing I thought was the ring crimp terminal on the wire might have to be removed to fit even the OEM boot because I thought it was put on before the ring terminal was crimped on at the factory.
This did hold to be true for the aftermarket, but NOT the OEM.
The OEM is clearly larger where it sits on the alternator and fits perfect. At first glance the aftermarket looks like it has a wider open for the wire, but the material of the boots are totally different.
The OEM is almost like a really super flexible silicone rubber. The aftermarket is much stiffer, with almost no give, like a bushing. There's no way the ring terminal would have fit through it.
With just a dab of grease (not needed really but made it easy) the OEM boot allowed the ring terminal to go through and sits perfect. No cutting or crimping!