Silver Boat:

You are right that the approved oils are for the new cars (1998 and newer). However, Mercedes also "recommend" the use of these approved oils in older model cars.

According to MB, the development and use of 0W-40 is to use only one oil in arctic or desert weather, i.e., everywhere. There is no need to switch oil due to temperature.

The key in the approved oils, to me, is that Mercedes does not like xW-30 or xxW-30 oils. As a matter of fact, Mercedes specifically say it and I quote:

"thin oils are not recommended, e.g.

Mobil 1 Tri-Synthetic 0W-30 (doesn't meet 229.1)
Mobil 1 Tri-Synthetic 5W-30
Mobil 1 Tri-Synthetic 10W-30"