Generally, Sprinter vans of that era often use a 15W-40 oil for diesel engines, but this is not a guaranteed recommendation. Using the wrong oil can severely damage your engine. The owner's manual will list acceptable alternatives depending on ambient temperature.
Do not rely on online forums or general advice. Check your owner's manual, and if you don't have it, you can likely find a digital copy online through a Mercedes-Benz website or a reputable Sprinter parts supplier.
