Advanced SLS -- I've searched can't find step-by-step diagnostics

[unity]

Hi guys-

I've spent a bunch of time going through the archives and I can't find a match to my conditions.

My SLS seemed to be working, as the ride height was fine, no sagging, but after I let the pressure out of the system - maybe 1/2qt of fluid - at the bleed port on the SLS valve, the rear end dropped way down and now won't come back up.
Before I bled it out it was holding pressure and the rear end had been riding fine over the month that I've had the car. The reason I started looking into it was that it didn't respond to load variation.

This is a new-to-me wagon. (83 300TD since for some reason it's not showing up in my signature at the bottom)
The PO said they completely rebuilt the SLS. There are new struts under there, the accumulators look new, and lo even the valve looks brand new. (They said it cost a small fortune to get the work done - after reading through here I wonder if they ponied up for a new valve...)

Anyway, at first the ride height was fine, no sag, but I noticed the fluid was low. So I ordered the right stuff and filled it up to spec. I was doing a few other things under there and the back was up on ramps so I was looking at the valve/sway bar setup and I started the car and tried to physically move the arm on the valve to see the action of the suspension. However nothing happened. I thought maybe there wasn't enough movement so I unbolted the connector arm to the valve and actuated the arm on the valve but there was no movement up or down. I was expecting to see movement as the valve reacted to the simulated change in ride height.
Since I didn't get any movement, I went through the archives and came out with the idea that maybe my valve needed rebuilding. So I ordered the O-ring kit from Andrew on here, and I went to remove the valve yesterday.
When I opened the bleed port, I got a bunch of fluid out, maybe 1/2qt or something, and then I noticed the rear end had completely sagged down - like a good 3" or more. Thinking it was maybe a simple bleed issue, since the valve looked new, I tightened up the bleed valve, poured the fluid back and started the car back up fully expecting to see the rear come back up again. But nothing. It stays sagging. Since it was riding fine before I took the pressure off the system I can't figure out what to think. I removed the return fitting from the top of the reservoir and put a container underneath and I'm getting fluid returned back to the reservoir at a fairly steady rate. I cracked the banjo bolts on the accumulators and there's fluid there...
Does this sound like I might have to do a thorough bleed of the system by actually loading it up (as opposed to just manually operating the arm on the SLS control valve?). Or does it point to a rebuild of the valve? (even though it looks shiny new?)
I've spent a bunch of time going through the archives and I haven't been able to find a step-by-step diagnostic to rule out failure of the various components. Any help greatly appreciated.

[unity]

the other question I had was - should I be avoiding driving the car with a sagging rear end - will that compromise the struts in any way?