MB is using Mobil 1 type synthetic ATF in their newer cars, and it doesn't degrade like the older ATF did. I suspect they are also using better friction material so there is less sludge.

However, I would change the fluid, including torque converter draining, and filter, at 100,000 miles.

I would NEVER "flush" an automatic transmission. Anything but fresh ATF in there is a serious problem waiting to happen. Note that "flush" often means feeding fresh AFT into the tranny with the cooler return line off, going to a bucket, so that the tranny pumps fresh fluid into the torque conveter -- this is the only way to change the fluid in an American auto tranny short of drilling a hole in it (recommended for many years by GM, they even left a thick, flat spot for you to drill and plug!). MB provides a nice drain fitting.

Peter

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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!