Having run into this the other weekend, I think the only way to do a complete tranny fluid change is to have th dealer do it. There is no TC drain on my 2000 C280. I was only able to get about 2.5-3 liters from a pan drain. The car is MY 2000 with 36k. Fluid was a reddish brown, still relatively clear, in pretty good shape as far as I could tell.

I would hope Mercedes recycles this expensive ATF if they use 12 liters with every change.

glenmore
1991 300CE
1990 LS400
2000 C280