I have used commercially available after run oil.
Also tried WD-40 which works (it does evaporate after a while).
A fellow pilot uses 1/2 kerosene and 1/2 tranmission fluid as after run oil. Haven't tried 3 in 1.

All seem to work fine. After clearing the engine of fuel drop a few drops in the carb. Flip the engine over smartly a few times to get the oil in the moving parts. Some pilots remove the glow plug to get better coating particularly with 4 stroke engines.

If you use the WD-40 be aware the engine can fire when flipped without the glow driver attached!!!!

I use heli fuel in my glow engines (2 strokes only) and add 2 ounces of castor to a gallon. I have engines that after several seasons don't show wear and run great. In the 4 strokes the 20/20 seems to work best. I only use after run when I won't be flying for a while.

EXCAP232