http://wd40.com/pdfs/WD-40_2000UsesList.pdf
Here is a list of things that WD40 can be used for that is also not listed on the can. I think you will find at least a few on that list about boat engines. If it can protect metal that is constantly exposed to water then why can't it protect a RC engine from a couple drops of water?
Ehroof please coduct your own test and report on the results. No matter what the results I can tell you I already know the outcome. Transmission fluid/after run oil will get milky if you add water and shake. If you let it sit the water will seperate back out. Your argument is simple "It advertises that it will work the best so it must be the best so I will only use that". I got news for you not everything always works as advertised. Hell, slimfast promised to make people skinny in a week ("give us a week and we'll take off the weight") but somehow we still have fat people walking around (not meaning to insult anyone as I am not as fit as I once was).
I also need to point out that your thought on transmission fluid destroying gaskets is also WRONG!!! Let me point out that every automatic transmission has an oil pan. There is a gasket that keeps you from losing transmission fluid. Somehow that gasket is not disolved when it comes into contact with the fluid. There are also many other gaskets and seals inside of transmissions. Wow, did you know transmission fluid can also be used to replace power steering fluid. I wonder how that can be when it does not list that as a use on the tranny fluid bottle. The people who bottle after run oil have found that if you label a common product for a special purpose you can charge more and people will pay it.
I for one will stick with what I know works and continue to use WD40. If I have none on hand I have some ARO in my box as a just in case. As for your good/correct advise. Telling peolpe they need to more spend more on a little bottle of your miracle oil instead of telling them the truth (other oils will work just as well) is neither good nor correct advise.
The best advice I know is this. Use some sort of oil to protect your RC engine after you run it. Oils that will work include and may not be limited to transmission fluid, motor oil, WD40 and other spray lubricant/protectants, power steering fluid, and of course after run oil. Just add some kind of oil to push the moisture away from the metal and protect it from rusting. No oil will stay mixed with water or absorb it. If it where to stay mixed with the water, than the oil would have a certain water content and that oil/water mixture would itself cause rust. This would happen because although the water is not visible to you or I it is still there as the oil has not changed the waters molecular structure.