From the same info I have saved, wether it is true or not, why spend $20-30 just for an addative for your oil? Here it is:

"Chlorine derivitaves and other chlorinated solvents are a great lubricant and were used for many years in motor oil before the destructive effcts were discovered.

When the chlorine from the lubricant combines with the hydrogen left over from incomplete combustion and the oxygen, these three things (and others) form HCL...hydro-chloric acid. Very bad for rings and bearings and such.

If left in the engine for extended intervals, creates a lot of damage.

Now...most engine treatments don't reveal thier 'secret' ingredients ('proprietary information' and all that jazz). A few are known to have excessive amounts of chlorinated solvents: Dura-Lube (the worst offender), Resur (a newer russian product),and the now-defunct STP engine treatment.

Rarely can any benifits ever be found with these additives, but even if there are benifits, they are always very short lived. Certainly lasting no longer than the length of the oil change interval, or possibly two. (50,000 miles with a single treatment? Only a fantasy, I'm afraid). They are certainly NOT cost effective.
'Marvel Mystery Oil' is considered to be an oil treatment, not an engine treatment. Some, but not all, oil treatments are good.
'MMO' is just plain and pure light-weight mineral oil. It's higher solvency ratio tends to help clean and lubricate lifters, promotes the removal by combustion of light carbon deposits in the upper cylinder area, and will even clean and (somewhat) lubricate fuel injectors.
A can in the gas tank once a month tends to help, as does a can installed with a fresh oil change if you have been guilty of not-frequent-enough oil changes.
Plus, it's cheap!
Z-Max, by the way, is nothing more than several bottles of plain old mineral oil, with a minute amount of food-grade dye added to give it a unique color. It certainly doesn't have anything called 'Linkite' in it, whatever the hell that is. What you can get from Z-Max for $50+ you can get from MMO for around $5.00.
Skip the engine treatments, change the oil and filter every 3,000 miles and you will save money and have a much longer lasting engine."