I used wd-40 for a long time, works great. The main thing your looking for is to not rust the bearings and crank, wd-40 displaces moisture. I really cant see how a couple drops of after run through the glow plug hole gets to the bearings. I shot the wd-40 in the carb on the box while turning it over after we are done for the day. I use Sidewinder fuel now and the motor looks great inside without after run oil.
Rex