doing the broken record thing
Since oil has many functions in the engine, so does or would an oil additive (in addition to the ones the manufacturer uses).
Corrosion resistance is one function of the oil and its additives.
Corrosion can come from water in the oil while the engine is not running (rust) and/or it can come from acids which build up in the oil from blowby of combustion products and maybe combined with water in the oil. H2SO4 is an example - suphuric acid.
Changing the oil is the only realistic solution for acids that form in the oil, no matter how they got there. Those acids can act on the metal in the airplane even while it is running. Oil additives can neutralize acids up to a point and then their capacity is exhausted and you get corrosion.
Water in the oil comes from water in the air condensing on internal parts when the dewpoint is reached and the dewpoint is a factor of temperature and absolute humidity - the amount of water suspended in the air. If the air inside the engine is dry then there will not be any water to condense.
Sadly, every time you shut down your engine, you create a rain forest effect because the hot air inside the engine has enormous capacity to hold water vapor and water vapor is one of the two major results of burning gasoline (carbon dioxide is the other). If you fly every day, then you have a good chance of re-coating the parts with oil before the oil film drips down and off. Who flies every day? Not I. Therefore the answer is to dry the air inside the engine before the oil film goes away. There are two approaches and several devices available and home-made is also very easy.
If you don't fly every day and if you don't use a dehydrator then my guess is that you will have rust in your engine. It's really pretty simple.
