Why would the suspension lean to one side?

The same air pressure is applied to both air bags so they should lift the same amount, however when the weight in the car is removed and the ride height is too high, the control unit opens the solenoids to vent some air. If the control unit only sends the vent signal to one solenoid or the wiring to one of the solenoids is bad, then only one would vent so the other side would stay high. Check wiring and connecters. If the air system is ok, it will still lean if of the car is heavier on one side or if one of the front springs is weak or broken. These are just guesses and I am assuming the limo is the same the cars I am familiar with. .

If the car does not have "air ride", Look for a broken spring, low tire pressure or a bad strut.

A broken Leaf spring would cause it to lean to one side.

ANSWER

Depending on what type of suspension you have (torsion bars, coil springs, solid axle,leaf spring, etc. It could be a worn spring( leaf or coil), broken torsion bar, or a broken steering knuckle .