Lucky you have the dipstick to verify the oil level. I don't understand what was so wrong with the old dipstick system, anyway.
You may have a sending unit going bad. That wouldn't account for the litre per 2000 miles consumption. Hey, that's not much, truth be told. I'd investigate the error message if it comes up again, and watch the consuption to see if it goes up over time.
And if you're going by the FSS oil change intervals, you might want to stop. Even with Mobil 1 you might want to buy some cheap insurance with more frequent changes.
1998 C230 "Black Betty"