Caliper seal kits are <$25. It's a fairly easy DIY job, or a couple of hours labor by a pro to rebuild the caliper and bleed the brakes.

However, you may just have a leaky hose or leaking bleed screw?

Good luck.

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold