Sorry to hear that.
This may or may not be of help
An issue I'm very aware of with both modern petrol and diesel Mercedes, in that if they have been used on short journeys for quite a while and have not been getting really hot then taken on a longer journey, the NOX sensor doesn't like it and the engine management light comes on and emissions rise, bad news at annual testing time.
I presume there are no error codes? Have you tried engine and exhaust cleaners and a fast Italian service run to get everything sinking hot and values down.
