It sounds like the oil capacity being quoted in the owners manual is the proper level just for the 4matic. I use 6.85 quarts, 1/2 a quart more than the 2 wheel drive motor, the pans are different due to the front differential being integrated into the pan.
The proper capacity for the regular 103 motor I believe equals 6L, which converts to 6.35 quarts. From my observation, putting in the factory recommended amounts does in fact put you between the high and low marks on the dipstick, not at the max level. As 400E mentioned, MB does NOT want the engine at/above the max line any more than they want it below the minimum.
I also agree with 400E on the oil consumption increasing if the oil is maintained near the MAX mark on the dipstick. It's hard to explain (in fact I don't know if I CAN explain it!) but it seems like MB engines will burn off the excess oil until it reaches the level it "wants" to be at, then it will stay there. I beleve that in some cases, this is what some of the problems are with the 112 engine everyone is talking about. To add to the problem, the engines (112's) are getting to the bottom of the operating range (near the min mark), then the oil level sensor is making the "low oil" warnings come on, when they're not even in need of it yet. If the owners would wait 5-10 minutes, then check the oil, they would see they are actually above the min mark on the stick, and may in fact be exactly where the engine "wants" to be for oil level.
(There, my "manifesto" for what's really wrong with the 112 engines ((in some cases))