I am trying to reverse engineer a problem with my car.,,

I did the head-gasket a couple of months ago. head was checked for leaks and straightness, but all was good....

I remembered yesterday that when i did this, my piston tops were covered with wet carbon. i literally cleaned them to a shine by wiping them with a rag.....

exhaust smells.... yes, but not sure how to describe it. most strong on first start.... their is very minimal oil consumption if any....

so generally speaking, what will would have caused this at the time?

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1993 300E, 2.8 M104 .....