Typically if the rear is changing height without loading or unloading the rear the valve is leaking. This holds wether the engine is running or not. With the engine running the rear can raise and lift without loading, and without the engine running the rear usually sags.
If the pump isn't working the rear won't lift when loaded.

I have the SLS Valve O-ring kits. If you need one or two kits let me know.

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