The above video was done by BeechTalker Joe Fischetti, with an amazing little "dental camera" that sells for just over $100 and connects to your computer!

The item is sold on  HERE for $116 as of 21 May 2011.

These are some of the kinds of images of valves that can be captured with this camera to assist you in evaluating the condition of your valve faces and seats. See the entire BeechTalk thread on this topic HERE. Images below also courtesy of BeechTalker Joe Fischetti.

This might be a good tool to suggest to your mechanic or if you are inclined to have one for your own use, I've not seen anything do such a great job for such a CSOB cost.

Joe advises that for better access into the spark plug hole the shaft of the camera needs to be modified or ground down a little. Here is how John W. tackled the problem. Ending up with heat shrink on his end product:

Nice job John!