I have this on my 99 sprint as well, and on the footpeg hangers. Mind you, mine has been in a dampish garage for the last 4 years so its not too much of a surprise.
The only way i can think of to deal with it would be to strip the swingarm off and either respray it or get it powdercoated. Mines not bad enough that I'm going to be doing anything other than getting rid of the corrosion and putting some polish or something on there to stop it getting worse.
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