Continuation from the last question - The oil was not burnt but wet on the threads and electrode
It sounds like your valve cover gasket has failed causing oil to seep past the gasket and down into the spark plug tube. Here is the link to the part needed: http://www.partsgeek.com/gbproducts/DC/6333-05228982.html?utm_content=DN&utm_term=1994-1997+Mercedes+C280+Valve+Cover+Gasket+Set+VR+Gaskets+94-97+Mercedes+Valve+Cover+Gasket+Set+95&utm_source=google&utm_medium=ff&utm_campaign=PartsGeek+Google+Base&gclid=CKHn0OTxrcICFQuSaQodolEAeg
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