I just flushed and replaced filter on mySDL so I don't know how similar ithe Process would be but it worked well for me.
I used my home built 12v electric topside pump to remove the old fluid. Get the fluid warm first.
1. Dissconnect the low pressure return line coming from the steering gear. I was able to discinect mine by releasing a spring clip that hold the hose to a hard pipe fitting that emptys into the PS pump sump. I disconnected it here because it was easy to plug the hard pipe quickly preventing fluid from flowing out and when you quickly elevate the return hose end you prevent fluid flowing out of that end.
2. Attatched my suction punp inlet the the return hose. A 3/8 OD polyethelene hose fit inside the return line perfectly.
3. Remove PS pump cover and start the suction pump. As fluid level in resevoir sinks stop pump when the filter is exposed and the fluid appears to be at the bottom level of the filter. You can look at the small space between the filter and the sump housing.
4. Remove the threaded stem holding the filter and the filter, replace with the new filter and reinstall the stem.
5. Top off the sump with new fluid. Start suction pump. the new fluid will be pulled thruough the pump, the presure line, the steering gear, out the return line by the suction pump.I pumped my old fluid into a clear 3 liter soda bottle. I kept an eye on the fluid level and added new fluid as the level decreasedkeep the level at 1/2 full. I had my daughter sit in the car and kept her turning the whell from left to right and back as often and far as she could. When the fluid coming out of the return line was clean, stop the suction pump. System capacity is 1.2 Qt. I think I used about 2.5 Qt. during this flushing.
6. Replace the PS sump cover, remove pump from return line and quickly place the return line back on ythe hard pipe fitting that you have just quickly reved the plug from. Replace the spring clip securing the return hose to the hard pipe fitting.
7. Remove the PS sump cover and start her up. Have some new fluid handy and add enough to keep the fluid level at 1/2 full if needed. Have your helper turn the wheel from stop to stopa couple of times. Let the fluid get warm and then fill to the proper level. I filled to 1/2" below the top. eplace the cover gasket, mine was hard and brittle. Put the cover on and your done.
8. I kept the cover on and sealed when disconnecting and connecting the return line inorder to use the inherent vacum to eliminate or reduce the flow of fluid out of the sump amd return line. very little came out of either during the process. I placed my finger over the hard pipe end immediately and then quickly placed a rubber plug over the pipe end. I used a small rubber protective cap from some other part that I found and that fit snug you could make one easily by using a short peice of the proper size hose that has one end plugged. I used an outside plug because I figured it would be quicker and easier than inserting an inside plug into the pipe. After the change the new fluid was not pristine, a small amount of the old fluid was mixed into the new but was infinitely better than the old. I assume that getting all old fluid out could be accomplished with repeated procedures. Everything sounds and has been working grear since. Some people blow off the filter stating that MB has eliminated them in newer cars but they filter only cost $2-3 so its cheap insurence for a PS pump or PS gear. My car may be different but the same procedure should work on most. Good Luck.