His air shocks are probably fighting the bind in the bushings or arch of the spring because it needs to be so high...
The right solution is the proper springs. Trying to do it with load assist springs is going to remain a constant disappointment.
The shocks probably don't leak in water because there's no load on them with the shaft at the same height too.
Want more pressure? Get a regulator and a nitrogen tank. If that don't do it, nothing will.
