I just had the same problem with the brakes on my 420sel. The passenger rear caliper started leaking after i did a brake job a couple months earlier. I was quoted $242 each fom the dealer, so I just ordered up a set from advance autoparts. They were ate rebuilt. It took me all of ten minutes to install each one and was back on the road leak free. It was worth it to me to just buy rebuilt ones with a lifetime warranty than to spend 500 dollars for the same thing.

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1984 300SD Orient Red/ Palomino
1989 560SEC
2016 Mazda 6 6 speed manual
1995 Ford F-150 reg cab 4.9 5speed manual