Check to see if the can has been opened.  If it has, there is a possibility that water has contaminated the oil making it susceptible to rusting from the inside out.  If this is the case I would dispose of the oil.

If the can has never been opened then the rust is probably limited to exterior surface rust.  If this is the case then I would "test" the integrity of the rust spots.  To do this I would purchase a bag of kitty litter, put it in a plastic tub and do your testing over it.  The Kitty litter will absorb oil in case of a leak.

The oil will act as a natural rust inhibitor so if the can is unopened and deemed solid then it should be fine.

As far as storage is concerned, if the can is constructed entirely of metal then a dry environment is key.  If it is the old cardboard and metal container, strive for a "happy medium."

Feel free to contact me should you have any further questions.  My grandfather revolutionized the two-stroke motor and I am quite familiar with them!

G.Krueger

Curator of the Lynchburg Museum System