Take a week off, do a search under "oil brand" and wear your eyes out. You need 6 litres handy to do it yourself, and most MB nuts use Mobil 1 synthetic and a weight that is suitable for their climate. However, not to begin a long winded debate as regards to synthetic vs. dino, brands, etc, I would recommend that you buy whatever you prefer, fits the budget, and the only thing we'll ALL agree on is that you change it often.
And you'll have more info than you'll even need.
1998 C230 "Black Betty"