What Dan said. Spend the $70 for a rebuilt caliper.

I've had a few stuck calipers over the years and have never had a satisfactory experience trying to resurrect them. Usually the piston is corroded and there is little can be done to adequately polish them.

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1981 300TD 310k miles
1970 280sel 172k miles
1966 230 Fintail 162k miles

"Where are we going? And why am I in this hand basket?"