Oxalic acid is a popular chose around here. There are many threads on the subject.

http://www.google.com/search?hl=en&b...4l1l1l0.frgbld.

Also, white vinegar works good for treating rust spots. Soak a rag in vinegar, put it on the rust spot. Then cover it with plastic wrap and let it sit a couple of days. Another thing I've done is used a dremel tool with a tiny wire wheel to clean rust off spots.