I used Marvel in my cropduster's for years. Av gas and in my oil. Aero shell w120 (straight 60 weight) marvel is a transmission fluid based solvent with a few lubricative additives included. The transmission fluid base is a cleaning agent therefor freeing up carbon fouled lifters, oil passages,and generally cleaning sludge in an engine. If you have greasy hands, pour some on and it will dissolve the grease and clean yor hands. With the advances in synthetic oils and proper oil change intervals, there isn't as much need for it now as our oil is not as "dirty" as the older stuff. If I bought a motor that I didn't know much about the maintanince, I would run marvel in it for a couple changes with the intent of cleaning it out. I ran it in my aircraft fuel to keep the top ends clean. After all, a Pratt and Whitney R-1340 is just a big nine cylinder Harley motor !!! Just my two cents worth.