Kent,

I would try to dissolve the rust (which is essentially Fe++ and Fe+++) with a chelator like citric acid.  An old home remedy for rust stains appearing in your dishwasher has been to run it with a cup of Tang - the astronaut-inspired "orange juice". The citric acid molecules in Tang form a "cage" around the Fe ions and solubilize them. 

An even better chelator of rust, if you can get it, is EDTA (ethylene diamine tetraacetic acid) a molecule which has 4 negative ions which surround the Fe (as opposed to citric acid which has two such negative charges). 

You can purchase Tetrasodium EDTA from Sigma:  http://www.sigmaaldrich.com/catalog/product/fluka/03701?lang=en&region=US

A 250 gram bottle is sufficient for 2 liters of solution - but I would bet that you will only need a quarter of that - and you will have a concentrated solution to repeatedly spray on your chain. Let it sit for a while (1 - 2 hours?) between applications/attempting to further beat on your chain.  The tetrasodium EDTA solution will have a fairly high (alkaline) pH  (10 to 11 on the pH scale, where 7 is neutral and lye (sodium hydroxide) is 14), so wear gloves and eye protection, and rinse off any skin contact with copious amounts of a dilute vinegar solution.  Use the tetra sodium version of EDTA, rather than the free acid form, as this will be the most effective at binding the rust ions.  Be sure to neutralize the chain afterward, as well as your chain compartment and bilge.

Unlike treating with muriatic acid (hydrochloric acid), you will not need to worry about fumes nor leaving chloride ions on your chain to pit it and cause further rusting.

Hope this helps.

Derick Gates

Brava - SM2K #400

presently in Sapphire Beach Marina

St. Thomas, USVI