I thought I was clever. I rigged up this flushing approach. Basically I removed the return hose from the reservoir, jammed this clear hose into it and clamped it. I slipped some hose onto the reservoir nipple just to keep fluid from falling out. A cap would have worked but I didn't have one. Then I just shoved the end of the clear hose into the top of the reservoir. I think the plan was to start the engine, let it recirculate and when I was ready, divert to a pan and try to gracefully refill the reservoir so it didn't run dry. This was not successful.
I think the idea is still sound but my god it was rife with execution errors. Ian started the engine for me and it seemed to be working. But then I guess the reservoir was pumped dry. This shot a slug of air into the system and by the time the air got back to the clear hose it SHOT out of the reservoir under pressure and sprayed fluid all over the place and made a HUGE puddle under the car. This happened so fast! And just as I told Ian to shut the engine off, I turned around to grab my liter of P/S fluid and it was TIPPED OVER on the floor and had leaked 3/4 of it onto my floor. TWO giant puddles of P/S fluid. I was livid.
By the time I had somewhat calmed down I realized I needed to run back to the dealer for some emergency fluid. I just don't know if I can use any P/S fluid from a parts store and this was not the time to do the research. So I sprinted over to the dealer and tried calling a bunch of times since it was like 3:45 and the website said parts closes at 4. They never picked up. When I got there, I ran in and they had closed the metal curtain for the parts counter and I was like NOOOOOOO. I walked over to service and was like "uh....any chance you could help me get some P/S fluid? I'm in a bit of a pickle." He walked me back over and said, oh, he hasn't left, he's just upstairs doing some inventory, he'll be back. And he was, thankfully.
I said, I'll take three. He goes "you can return what you don't use." I said, oh that's OK, I'll probably just hang onto it. He asked if I had other Mercedes because I guess this stuff is used in the ABC system and some other hydraulic fluid purposes. Then he said "OK, that's $34/liter." Ah, now I know why he made the comment about returning unused stuff. I may still do that...
Back at home I abandoned the flush plan and frankly a whole lot was on the floor anyway. Actually thinking about it, if I was able to shove a funnel into the reservoir I might be able to fill it and let that act like a bigger reservoir and keep it all topped off as the pump moves a ton of fluid around. It was pretty much a fill, jack up front end, turn steering wheel back and forth a couple dozen times (Ian did this for me), add fluid, clean the giant I made, affair. Actually I ended up having to bleed twice because I guess I started it prematurely because it seemed to suck the reservoir dry. Great.
Anyway this is the normal process, same as I've done on my Caprice, CTS-V, STS and SRX.
I haven't driven the car yet but I think it will be fine and at least I did actually get a bunch of new fluid in there.