I drain and fill the reservoir every 10k...seems to keep the fluid clean, and it's certainly easy. Will do filter maybe every 60k.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 159k miles
06 E320 CDI "Rutherford", Black on Tan, 178k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 75k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Humm, I have an old post from a guy on the MB news group that claims he opens the lid of the pump, drains the steering box and refills the pump, no problem. Claims the drain plug is "in the middle and aft and pointing slightly back on the bottom of the steering box", If it wasn't the cocktail hour I'd run out and see

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

There's one on mine. No sense in draining though, pushing a gallon or so through (wiki method) while turning wheels to the hilt slowly left, then right does the trick.

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327K on 1986 W201, 602.911, 722.414 2.5 190D ("The Red Baron")
139K on 1993 W124, 104.942, 722.433 2.8 300E ("Queen")

http://farm5.static.flickr.com/4081/...0bb92d3c_m.jpg http://i370.photobucket.com/albums/o...g?t=1325284354

Do not worry about your difficulties in Mathematics. I can assure you mine are still greater.
- Albert Einstein

take a walk down memory lane...

I've always just drained the reservoir, pulled the return line, put it in a bucket, plugged the return connector, filled with fresh fluid, then turned the pulley by hand until clear fluid exits the return line.
I've never turned the wheel lock to lock. I'm always afraid to let air damage the pump with the motor running. and it's difficult to turn the wheels without the motor running.

when I did mine I put the front end on jack stands, and with the engine off I turned the steering wheel back and forth. This cause the fluid to drain fairly quickly but was manageable with a gallon milk jug (in the place of the washer res.) with the low pressure hose stuck in it.
I went through 4-5 quarts including the what was left in there.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg