Although I'm a "newbie" here - been doing this over almost 13 years now so I'm not new ot the hobby - TimK and parris are absolutely correct on most points.
Point one, EVERYONE likes to argue over ARO.

I think it's second only to the nitro percentage argument.
Point two, WD-40 is indeed a WATER DISPLACEMENT oil. If you go to their website, you'll see it got it's name because it's the 40th and final formula created for that purpose.
Point three, remember why you use ARO in the first place. Tha alcohol-based fuel we use is hygroscopic, which means it attracts water from the air. The purpose of after run oil is to displace water from your engine internals so that it cannot condense on the parts inside and create rust. In that context, WD_40 will **work** for ARO, but the correlary to point three is . . .
You don't even need to use ARO if you run every day. It's only necessary if it's going to sit more than a day or two. The reason people recommend using it after every run is because you never **really** know when you're going to run next. So it's a very good idea. However . . . this is also why WD-40 is not the BEST choice.
WD-40 also contains solvents and acids. Over time, the solvents evaporate, leaving a gummy residue, and the acids can etch surfaces on a microscopic level. I don't know about you, but I don't want any etching going on inside my engine.
Point four: no one knows the true makeup of manufactured ARO's except their manufacturers, but your guesses are probably close to it. The mystery of Marvel Mystery Oil is indeed given away by its waxy smell, which tells you it's a paraffin-based synthetic. Many ARO's smell very much the same.
Point five: when all else fails, ask the manufacturer. OS engines backs up your statements on two points: one, that a recommended sub for ARO is 50/50 ATF and MMO, and two, that 3-5 drops in your crankcase are next to useless, unless that's all your crankcase holds. The idea is to completely rinse out the engine with the oil and drive out all alcohol residues. I use about a half teaspoon, down the air inlet only, cranked over a couple times on the starter box. You don't need to remove the glow plug and put it down there, all that does is make you suceptible to getting dirt in there and further scratching up the gasket, which can lead to compression loss. Besides that, anything you put down there will blow out the exhaust port anyway as soon as you turn it over. Let the ARO find it's way through your engine the same way the fuel does, through the air inlet and with a few cranks on the starter box (or pulls on the pullstart.)
Point 6: ATF
HAS to be a water displacement oil. If you've ever gotten water in an automatic tranny - you'd know the truth of this, for I have.

A 50/50 mix of MMO and and full-scale automatic transmission fluid will give you a triple-lifetime supply of ARO, that is what I've used for years.
Watch for an expansion on this article on my site.
