Naval Jelly will dissolve the rust chemically. After that treat with a corrosion
Inhibitor like ACF-50 (my favorite). It is not as cheap as WD-40, but is magic IMO. ACF-50 will stop the advancement of corrosion on contact.
I have been using it for years in aviation and on all of my equipment.
Here is a link where you can read about it, but you can find it cheaper.
I have no financial interest in this product, I just think it is the best.
http://www.amazon.com/dp/B000P1C8UO/...l_8xg0tnl5kp_b