Yes, the fuel these engines burn is the worst thing you could leave sitting inside a engine, Hydroscopic means that it absorbs water out of the air and the methanol in glow fuel is very hydroscopic.  Castor oil will do nothing to displace the water and tends to gum up if it sits too long.  I agree with the airtool oil or trans fluid.  Transmission fluid is one of the best oils we have.  What I do at the end of the day is run the engine out of fuel at idle, then give it a good squirt of WD40-  the "WD" stands for water displacing which is a good thing, then run a few drops of air tool oil or trans fluid through it and you should be good to go.