Do you know the mileage on your Engine?
If you believe the Piston Rings may be sticking Soaking in Marvel Mystery Oil may help.
It did on my Volvo that had grey Smoke all the time after it sat a year and I drove it 6 months with a Thermostat that was opening too soon (my compression is also good).
Members have siad that using Synthetic Oil can free up Piston Rings but it takes about 200-300 miles of driving.
Have you done a Valve Adjustment.
Could be your Injectors need to be checked.
Valve Stem Seals? A bit of work but not expensive to replace.
For more details on the above stuff:
DIY Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum
PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles