I need a used wiper relay for a '92 500SEL. Part no. 140 542 00 19 Or, if anyone can tell me how to open one of those puppies up without ruining it I think I just need to correct some pitted relay contacts.

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1996 SL320 97K miles
1996 C220 130k miles
1992 500SEL 170k miles <---sold
1986 300E 216k miles <---sold