Get some Kroil Oil, take a Popsicle stick or a Starbuck's stir stick. Put some Kroil Oil on the rust... allow to sit for a couple of hours to penetrate and then gently but firmly rub with the stick. Be sure it's NOT hard wood.
I just cleaned up a rusty Model 54 that way and it works wonders and does NOT cause any damage to the finish (that still exists).
You can get Kroil Oil either at a hardware store or Brownells.
Do NOT use Steel wool or any abrasive material to it, it takes the finish off.