I checked with MBNA today and according to them, oil weight recommendations are not in the manual given with the 99 E320.
On the other hand, they were no help either. They siad that MB recommends not using synthetic oils and then allowed that Mobil 1 comes in the AMG engine cars. Then they siad Mobil 2 was OK, but other synthetics are not. They siad 5W-30, 10W-30, 0r 15W-50 were OK too. Back to square one.
Does anyone know what happens if you mix weights, e.g., does half 5W-30 and half 15W-50 give you 10W-40 or just a mess? :-)