A note on the "dreaded green coolant" -- it has less corrosion protection than Xerex G-05 or the MB coolant, and the anti-corrosives tend to precipitate out into insoluble complexes in the presence of aluminum. I've seen this personnally -- my sister blew a head gasket a couple years ago on her Volvo 740 Turbo on the highway -- there was corrosion on the head so bad there was almost nothing left at the combustion chamber seal.
I do no know when of if the coolant was ever changed, and there was so little left I couldn't even tell from the odor what condition it was in (no top of being cooked. like the oil), but I'm using Xerex G-05 in all my cars as I change them out.
Very long engine life is an expectation in Europe, as people tend to keep cars much longer over there. MB (and VW, etc) have spent quite a bit of time and money finding ways to reduce or eliminate corrosion problems, the main killer of aluminum rads. I'll take their advice.
You may do as you please.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!