Castor oil by itself will gum up after a long period of time. We use castor oil in our model airplane engines and over time, what is left there after the fuel (alcohol) evaporates, will seize the carburetor barrel when it dries out. Alcohol will -re-constitute it - thus alcohol will clean it from your bore if the borer gets gummy.
The synthetic motor oils are good - Amsoil 2 stroke oil - the 100:1 mix was perhaps the best, but I haven't seen it lately. It did not gum a modern rifle action or bolt down -35, at any rate.