OK narrowed to solenoid valve for the left rear shock as the leak-down source, but now Im asking if the vent valve is in the shock or the manifold block. Im imagining the air bag solenoid is internal to the bag where the wires plug in, and the other solenoid is in the block. And the valve causing the leak could be either one, the fill valve or else the vent valve. It seems either one might cause bleed down. And to replace the one in the air bag this means replacing the bag.

So no wonder the first step is often to just replace the solenoid block with the manifold. Seems likely..