I'm sort of surprised no one mentioned this, but glow fuel is mainly alcohol. While it also contains some oil most if not all alcohols will absorb moisture from the air...and I believe a cooling engine will increase this affect as it cools. The ball bearings in motors like the OS 46AX are not rustproof, and while I am fairly new to the hobby I have seen and heard of a number of cases of the rear bearing rusting fairly quickly. Fayrwerks experience is not unique. While I do not have enough experience to have an opinion as to which oil is best, I do use After Run Oil. I fill the carb with the throttle closed, then open it to dump the oil into the morot. I then give the prop a spin with the electric starter to give a fair chance for the stuff to actually reach the rear bearing. So far, after eight months of flying two or more times a week for at least a total of one hour each time there is no sign of bearing noise.