I've heard great things about evaporust. I've never used it but it's supposed to be very acidic and do exactly what you've described.
I use a small ultrasonic cleaner w/ various solutions. Eats the rust away and leaves parts looking brand new. Harbor Freight sells the model that I have for under $80. Depends on how large the parts that you have are but if they fit, it's a great way to do it.
