Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Sounds like you don't drive this one very much, 10 years old 10000km.
To me that says cold starts, short trips, little engine temperature etc.
All contributing factors to larger than normal carbon buildup within the combustion chambers/cylinder head ports.
I have many cars in the same scenario as yours, and have fixed many with an "upper cylinder clean".
Are you using the recommended premium unleaded?
How have you gone with your problem?
I hope my advice has been of assistance to you.