Although there are many oils with a C rating, and probably the ones that don't have it on the can, could probably pass an early C rating test, the universal grades are much better suited for diesels. They contain a greater amount of cleaning agents and additives that can disperse the soot better. After all, these oils have been developed specifically for diesel engines.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in