With the nitrogen chambers "water logged" the systems get destroyed. I have seen many where they are in effect deflated due to the pounding. I'm not sure how it actually happens but like the others have said the replacement of the accumulators allows the systems to refill and work again.
I would suggest that anyone owning a load leveling system replace the accumulators every 100k miles and don't wait for the obvious symptom. Way before it can be felt the loading is tearing the system up. If the shocks aren't leaking they will live again.
Bosch Master, ASE Master, L1
33 years MB technician