If you can get your hands on some Naval Jelly, apply it with a brush, leave it on 15-20 minutes and rinse it off. If the rust is extremely heavy, apply it several times and leave it sit out longer before rinsing (even overnight). Lubricate once rust is gone. Navel jelly is a miracle worker when it comes to rust. I took a deep sea fishing reel that was so rusted the gears woudn't turn and when I was done, you couldn't see a spot of rust and it worked like new. Just don't get it on your hands!
Good luck, George