The "O" rings around the neck of the solenoid dry out and when the solenoid is removed from the air spring they must be replaced or they will leak. The air line that goes into the solenoid seals by contacting a small "O" ring down inside of the solenoid. If by chance the air line was cut it must be inspected for any burrs and the cut must be perfectly square to the tube OD as it is pushed against the "O" ring. These "O" rings on occasion need to be replaced as well.
You may be noticing one corner high as it is trying to compensate for the side that is leaking. There is only one height sensor in the rear, unlike the front that has two. You could also have a leaky front spring and this may also be causing the rear to over compensate. Be sure you get on a level surface and then measure the wheel lip height all around to see if it is level. The correct height is around 27.25 " from the top of the rim to the top of the fender lip, at the wheel center line.
