Originally Posted by
Mr. Spadoni
But where would I find a boroscope?
I have one (endoscope), you can pick up a cheap USB one on the interwebs.
It's worked for to inspect seat and down tubes, but the vent hole for top tubes is typically too small to fit. Of course, getting it up into a seat stay would be impossible, as the head of the boroscope is 5-6mm in diameter.
Replacement of a seat stay isn't too difficult, I've done it before.