Warning: I am assuming that the w124 SLS system is functionally identical to the w123 system. (Having looked at pictures of the SLS valve it looks identical, except its a different shape.)

When you rotate the valve lever arm CCW it allows fluid to enter the lines running to the actuators (and from there to the accumulators). When the arm is in its neutral position the fluid path to the actuators is sealed off (this is how the system is most of the time). When the valve lever arm is rotated CW it allows fluid to bleed out of the actuators. The system does not actively pump anything to lower the car, as is evidenced by the fact that you can lower the car with the lever when the engine is off.

The car will only lower as much as the weight of the vehicle can compress the springs. The normal ride height of an unloaded vehicle is supported by the springs alone. Any car that goes lower than its normal ride height is either loaded down (and the SLS sytem doesn't work) or it has weak springs (and the SLS system doesn't work).

If I understand you correctly, your car will raise and lower (to normal height), but still feels bouncy after replacing the accumulators? Also that it doesn't raise up when the springs are compressed with a load.

If these are the correct (and only) symptoms, then I would guess that your pull rod (adjusting linkage) is too long and that the "normal" position for the SLS system has been set below the actual normal ride height.

Also verify that your actuators aren't leaking.