That's a good price, Kevin - for both the bike and the panniers.
I'm also pretty sure the rad will be in good nick.
I measured the gaps in the stoneguard and its 5mm. A pencil is about 8mm.
However, the stoneguard - radiator gap is pretty small, and may well be the around about the focal distance of your endoscope, so juist sticking it against the guard may give you a decent image.
Here's my attempt with a phone. I can't get the phone into the bottom area easily - because the phone is wider then the guard area, and its the bottom area that gets all the crud of course.
The radiator looks better than this when exposed, so don't be too put off -
(see here)Top area - clean, no folded fins, no cement-like accumulation, no corrosion:
Bottom area - some flies and gunge, etc, and this is after a clean about 200 miles ago.