Oxalic acid can work magic sometimes. Simply cleaning with degreaser and then cleaning with wd-40 and then ample lubrication can work wonders also.
You might consider just buying a new and cheap chain, since that is probably the worst offender.
jim
__________________
Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
--------------------------
SB forever