Did you ever identify where the leak was?

The purpose of the SLS valve is to compensate for changes in ride height cause by increased cargo load by adjusting the overall length of the actuators. The vast majority of the time the SLS valve is in its closed position. It only opens when you increase or decrease the cargo load in the car (the valve opens far too slowly to respond to road bumps).

Having said that, you can look at the actuators and accumulators as a closed system while driving.

Hydraulic fluid is incompressible, nitrogen gas is compressible. Normally, the fluid in the actuators is able to flow out the top of the actuator through a hose into the accumulator. The accumulator is a metal sphere with a rubber diaphragm in the middle. The diaphragm separates the hydraulic fluid from the compressible gas (I believe it is nitrogen). When you hit a bump in the road, hydraulic fluid is forced out of the top of the ram (through the hose) and it pushes against the diaphragm, compressing the nitrogen. It is the compressible gas in the accumulator that absorbs the bump and acts as a shock dampener.

Harsh ride like you describe would seem to indicate that the actuators are "frozen" (i.e. they are unable to compress rapidly in response to road bumps). Off the top of my head I can think of three possible causes: 1) damage to the actuators that cause them to bind, 2) a kinked or blocked hose between the actuator and the accumulator and 3) no compressible gas in the accumulators (failed diaphragms or leaking cylinder).