As long as I have been flying, the myths and legends surrounding Mavel Mystery Oil are ever present.
This much is true: MMO is not an approved additive for fuel or engine oil in any type of certificated aircraft engine. Period. For experimental aircraft, you can use it by the gallon but you have entered the realm of the true test pilot. Good luck with that.
As with prescription drugs, their is no such thing as an additive without side effects. Remember Mobil 1 oil for aircraft? It had lots of engineering behind the product but still was causing lots of problems. Do you really know what MMO is doing inside your engine, oil or fuel? If you have some very expensive engineering data for us to review, please share. Otherwise, the wonders of MMO are right up there with Yetti sightings.
As others have suggested, fly your aircraft often and change oil and filter every 25 to 50 hours. Use an approved aircraft engine oil. Many engineers and oil companies have examined and tested these products for their use as specified. Can you say that for MMO?