I wouldn't put anything into the oil that has solvents in it and run the engine hard or at high rpm.
MM-Oil contains Benzene, Mineral spirits and Naptha.
Idling in the driveway or short trips around town may be alright.
I know MM-Oil recommends it on their label and many use it in their oil, but its rather a gasoline additive and valve lube.
Oil thinned with solvents cleans alright, but doesn't lube very well.
In some cases, the oil pump screen can get clogged with sludge that has not disolved all the way.
Diesel motor oil, like Rotella or Delo, has 50% more detergents and 100% more dispersants than gasoline motor oil and is a better way to clean an old engine. It works slower and milder and cleans well over the long run with more frequent filter and oil changes than normal.
I got Rotella in both my daily 235 and even the new 261, year round.