One must consider the fuels used for different “venues” of operation. Airplanes are operated in relatively dry environments as are cars. As such, fuels have different lube and additive packages in them. Boats are a different animal and as such, fuels for them are formulated a bit differently for a number of reasons. This is the main reason why you will see differing conditions internally when ARO isn’t used and the engine is stored a long time. I don’t use ARO for short term storage, but 1 year or more gets a healthy dose of oil. I’m not picky on what I use - sewing machine oil or ATF works splendid for me. The engine I have pictured has 3-4 gallons of 15% nitro 20% oil (70/30 blend of castor/Klotz respectively) fuel through it with zero after run oil used. Still turns freely and smoothly. End of day operation and storage regimens will have differing results. The most important thing IMO is getting the fuel residue (and moisture byproducts) OUT ASAP. Acids are formed when synthetic PAG oils break down in the presence of water, and add to the fact methanol gets more corrosive being moisture laden, and so on and so forth.... Its not rocket science, but does require a little bit of forethought to maintain model engines.