[rotorwrench]

The stuff is a mix of plain mineral oil and a solvent. If you smell a whiff of it, you can detect the solvent odor. This stuff's claim to fame is simply how it reacts with hard carbon deposits. It takes it a little while but it will soften hard carbon to the point that it will not longer hold a bind between a valve stem and a guide. This is what it was made for and it is still used to this day on engines that had problems with sticking valves for one reason or another.

It was popular in general aviation for all the owners that had the small Continental engines of the 4-cylinder air cooled variety from the A65 through the O-200 series as well as several others. They loved to stick valves and the MMO was the cat's meow to get them to stop and it still is.