My OE MB SLS fluid bottle I had was red that I used to top up...

Just now I tested the valve leveler.
I disconnected the leveler from the sway bar bracket, started the car and nothing happened.

Moved the lever up, (it moved without any force needed)...then as it reached the top pressure started and it wouldn't go up any further. Still no movement from struts. Then tried to move it down -- this time it had resistance and once it hit the neutral position, I felt and heard a pressure release "hiss". No movement still. Then I returned it to the lower position, no resistance again.

I left it at each position for about 60seconds FYI.

If the car is on its jacking points the suspension will be hanging free, so nothing will happen.
You need to have the wheels on blocks/ramps with the rear suspension compressed carrying the weight of the rear end before moving the linkage will do anything I think.
You just need to have a good amount of clearance between the underside of the car and you, so if the rear end drops you are safe...

So since I have previously loaded the rear while on the ground and it does not rise, could air in the lines stop the system from working entirely?

Can we assume my leveling valve is the culprit here?
Are there any other items that I can do to test the pump or since I am getting a pretty good flow on the return line, can we assume its ok?

I would like to build a gauge to check my pressure. I could either do a T-line where the high pressure hose meets the hardline near the exhaust, OR at the leveler valve.

Does anybody know what the fitting(s) is/are? Any thoughts on either method? Anybody done it?

MB Gauge expensiveeeeee...phew!
Looks like its gotta be capable of doing 133bar/2000psi.