I was thinking of checking with the local hospitals and seeing what they did with their old ones............. but maybe starting with a clean one would be better.Is it possible to get an endoscope camera up in there?
I have used mine on several things like this and it works well.
There are cheaper. This is just an example. Do your own shopping.
Actually, I had considered one as long as it would fit through a spark plug hole. Could have used one a few years back to help diagnose a #8 cylinder issue on a car, and even now, have one that's a bit suspect and would like to look inside and examine for carbon or valve issues.
Cheaper isn't always gooder - my wife would tell me to send back a cheap one and try again.