First let me say that I am not advocating that anybody should use Marvel Mystery Oil. Being intelligent humans, you must make your own decisions. Remember that additives have a very narrow use range and many can do more harm than good if used without common sense. Most can be considered a complete rip-off since they do not have the advertised benifits.
Marvel Mystery Oil has apparently been around since the 1920's and was recently aquired by Turtle Wax. The U.S. Military contracted to buy huge quantities by the time of W.W.II. It was used extensively in airplane engines as a so-called top cylinder lubricant, and was also used in the land vehicles to keep the engines cleaner.
Marvel Mystery Oil was never F.A.A approved as similar formulas that came later were. Although not sanctioned for such use, it is still widely used by private airplane owners around the world. It is also often used in speedboats, perhaps because of the outrageous cost of engine repair.
Unlike other common additives, Marvel Mystery Oil contains chlorinated hydrocarbon oils. This makes Marvel Mystery Oil capable of dissolving contaminate buildup much like the acclaimed Berryman products, only at a slower rate and while still maintaining an oil film.
As an oil additive, it will help dissolve varnish and sludge. As a gas additive, it will dissolve that gummy stuff in the intake and break apart carbon deposits. Keep in mind that in a fuel injected vehicle, the gas goes in after much of the deposits. A special oil injector is required to clean the areas before the gas is injected. Small airplanes often use an oil injector to keep the intake clean and to keep carbon from building up on the pistons and valves.
As for the question, 10% dumped in the oil is fine, the instructions are on the container. The only thing I would add is that I use 10W30 to offset the thinning effect it has on the oil.
