Yeah I have one of those borescopes and it was no help. our house is insulated with paper rolled out and then cellulose sprayed on top of that. Can't get the scope up through the paper side of the insulation. It's also why we can't see where this thing died, it's just absorbing into that paper. I did take one of the exhaust fans down and the good news there is the little flapper to keep hot air from blowing back inside had gotten stuck at some point. So I cleaned it all up and that is working again, but still no clue.
Ended up calling a guy who says he will come out and find it. "or if I can't find it I won't charge you to remove it". Gee thanks. $150 to come out, $150 to get it and clean up if he finds it. I'm certain he is going to step into the 145 degree attic tomorrow, look, and say "nope, can't find it" and I'll still have the smell but minus a nice steak dinner. Fingers crossed he finds it, and if so that's one of the better $300 I'll spend.