This may sound like a questionable practice but the way I have done this on W123 Diesels is to siphon out the reservoir, change the filter, then take the return line off the reservoir and direct it to an old coffee can that fits in the area, then have someone like my wife or one of my kids start the car while I carefully pour new fluid in, maintaining a little fluid over the filter, until the stuff coming out is clean. Then I shut the car off and put the line back and fill the reservoir, run the car, check it and top it off if it needs it. Job done.

My 190E 2.3-16 has too much stuff in under the hood to do that and I have therefore had the dealer change the fluid and filter. I think they do something similar, probably on a lift, and disconnect at the power steering box. If you have a lift or can get under the car to work on it comfortably, this is probably the easiest way to do it without using too much fluid, and it really allows you to flush the crud out. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)