Whoever services your car should note the type and grade of oil used in your service handbook.
For instance, my C270cdi has had Shell Helix 5W/40 and Castrol 0W/30 put in her by various MB service departments.
The oil must be suitable for a diesel engine and meet the required MB standard...229.31 is required if a particle filter is fitted otherwise 22.9.3 or 229.5 can be used