As for the recommendations to use Mobil1 or another synthetic oil....True enought hat they have been shown to pass industry standard tests for rust prevention (as have any petroleum based oils meeting the industry specs) when the engine is subjected to a certain set of conditions not applicable to engine storage, but this is far from the same thing as a rust preventative oil for engine storage, which will meet a different spec, and one that is not commercially available, but is available for engine storage (under a Military specification) in the Arctic. Completely different additives are used for Mobil1 (and other oils) than for rust preventative oils. Go with Marvel or one of the air tool oils.

Then again, if you are using a YS engine, don't use any of the 'recommended' oils and only use what is recommended by YS.