ARO (After Run Oil) should be usedevery time you shut the enging off it's just good practice. But the thing is if your going to be driving the vehicle every 3 or 4 days then ARO is not really needed. I have left engine's go without ARO for quite a while and experienced no rust build up when I tore them apart, to clean them. As I said it should be used but it is not really needed if your going to be driving it every 3 or 4 days but if you dont know when the next time you will be running it it's best that you do use ARO. By the way if you get tired of buying the expensive ARO you can go to your Local Auto Parts store and buy some marvel mystery oil (air tool oil is what I use) it's the same thing but it's not colored like some ARO's are.

As for the Alcohol drying and leaving water no thats not true. The alcohol actually attracts water and if fuel is left in the enigne that fuel that is there will attract water and if left there long enough it will start to rust some of the parts such as the bearing, crankshaft and the cylinder lining which is not good at all in any sence. But I suggest against putting ARO in the Glow Plug hole. As a lot of dirt tends to get in that particular area and if you take the glow plug out every time and put ARO in that hole you dont always hit the hole and a lot of it gets on the side of the head which will carry foreign objects into the engine which again is not good. As that will cause scaring of the engine's internals, I just suggest putting it in the carb and turning the engine via the starting system obviously without the glow plug heater on. Most say about 3 to 4 drops of ARO is good, but I put a little more in and I never have a problem with fouling glow plugs. But you do what you feel is safe, everyone has there own little tricks.

PS. If you really want to put ARO in the Glow Plug hole a medicine dropper for kids works really well from what I am told if you still want to go that route. But I cant imagine that eliminating the whole dirt falling in the hole problem. I hope I helped