Here's the latest:
Our MB Factory Authorized Service- Shop Foreman has spoken to 4 technical specialists at his regional meeting and has passed me this information:
+3 of the 4 technical specialists have indicated that this condition is normal.
+1 of the 4 technical specialists suggests using General Motors Top End Cleaner (in motor oil) since condition may be caused by a piece of carbon stuck somewhere.
hmm....I recall reading a few posts here about resolving carbon issues in a 500E and will review to see if this E320 case may be similar.