Well, a handful of questions have been hanging here, so I will take a shot:
Check the fluid level in the reservoir. Should be in the mark on the little dipstick.
To check the system, measure the height of the rear of the car, then load the trunk with soem heavy things, (bags of mulch, friends, etc). Start the car and see is the car returns to the same height.
To test the valve, try manually moving the actuator while the car is running. If the car moves up and down, it is doing its job. If not, you know something is not working, not necessarily the valve.
When my cells failed, opening the bleed screw on the level control valve resulted in a foamy fluid coming out. This may help you to check the cells. If you get foam, at least one cell is bad.
I don't know how to check the pump, other than looking at the reservior while the car is running and observing fluid moving around. Maybe someone else has a hint on that.
My car has 150K miles almost, and all that has been done is replacing the cells, and repairing the hose that wraps around the engine, when it wore through. Maybe you will have this kind of luck.
Take a look at these things, and post some more questions. I will try to help you out.
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)