Before using something to prevent future rust, you might try spraying in some "Metal Prep" from the hardware store, and letting it soak well, then drain it all out. Don't rinse it with water, but let air dry. Metal Prep is a solution of phosphoric acid (& probably other stuff), so it's best to keep it off the paint (won't harm really tough paint like Imron though). The phosphoric will eat away all the rust & leave a gray/black coating on the bare steel. Once dry, then use your Framesaver™ or linseed oil, whatever.

Works for me.