MMO certainly has its uses. I use it to preserve carburetors during storage, and have often dumped it down the carb of a running engine just prior to shutdown to coat the intake and cylinders for long-term storage. I can believe its a safe solvent for slow engine de-gunking.
But why, please tell me why, would anyone put an octane-reducer in fuel on a routine basis??? Light oils of any sort SIGNIFICANTLY suppress octane. As discussed on another thread here very recently, distillates like kersone and diesel have octane ratings in the ~40 range, compared to 87 for unleaded gasoline. MMO petroleum distillate content is certainly similar, and in any concentration that could have a lubricating effect it WILL also reduce the octane rating of the fuel appreciably.