After a compression check, I had one cylinder that was way low. So I just pulled the heads and noticed at the bottom of that cylinder there is what looks like a form of corrosion that has the appearance of what metal looks like when eaten by an acid. The section of the piston that was adjacent to the that section of the wall was covered with a whitish film that readily wiped off to leave a clean piston surface under that section that was covered by the film.