Check to see if the air is blowing right through the cylinders. A bad O-ring inside will do this. One way to check cylinder is to hook up lines to one side, pressurize it, and submerge cylinder in water. If air comes out the other nipple the piston seal is bad. I had this issue with a set of Century Jet retracts this Spring.

You  can cut your looking in half if you can establish that it only leaks in the up or down position.

Chuck