Is it leaking from the front seal? Do some research - you can usually replace the seal rather than the whole compressor. Would be a lot less expensive, and there's no point replacing a compressor that's still capable of producing 325 psi.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280