I used to look inside them with an Olympus Endoscope with flexible magnifier tip, when I was in the RAF ... That's what we used to use to check inside Gas Turbine engines to check for damage.
If it's done less than 60-70K, I'd not go to all the trouble and expense. There won't me much to gain. The tool we used was a Ford Special tool made by Churchill (now SPX) and was like an open-sided deep socket that located over the cap. It used a mount bolt as a fulcrum, and had a long handle as a lever. We substituted the line method, as it seemed to be quicker and more reliable. Cant damage anything, and you don't need compressed air. You leave the end dangling out, so you can pull it out once the piston's down.
Good luck, whichever way you go!