Typical accumulator breakdown occurs when gas chamber section has been compromised.
This causes pre-charge gasses to escape into fluid section and eventually fail to provide enough accumulator back-pressure for system to function properly
Things that could lead to failure are
Foreign matter in fluid causing excessive abrasion on o-rings or bladder eventually causing tears or gouging to o-rings.
Incompatible fluid vs seal material, the material used must meet fluid and temperature requirements of system. without knowing material it is not recommended to change fluid types other than what was suggested by manufacturer doing so could speed the deterioration of accumulator seals and
increased cycle time.
If system is not designed correctly the bladder or piston o-rings will be put in a position where they are running a full travel cycle too frequently, this in turn will cause seals abrasion to happen faster than normal and lead to premature failure.
Automotive accumulators are typically sealed units and do not allow for gas recharging or adjustment in gas pressure. Also they are not designed as a rebuild-able unit, the unit is sealed for life and needs to be fully replaced when failure occurs.
Rebuilding a sealed accumulator is a destructive process and will change tolerances, even if you mange to reseal unit, the sealing surfaces are most likely compromised and susceptible to premature failure .
In general bladder accumulators tend to have a higher failure rate than piston types, in allot of cases this is due to bladder diaphragm flexing, over time molecular structure of material changes and creates a weak-point.
typical symptoms of accumulator failure causes hydraulic pump to stay on longer to maintain system pressure, when pump shuts off and system tries to utilize accumulator reserve pressure there is sudden drop to bellow pressure threshold and pump will be reactivated prematurely to increase pressure.
Failure to diagnose and remove a bad accumulator will lead to abuse of pump section and premature failure of pump section components.
The accumulator should have enough capacity to provide multiple system activation's before it needs to be re-primed, this allows pump section and motor to have a good resting period before it is called upon to re-pressurize system.
Testing of accumulator should be done by specific test procedure to determine accumulator backpressure.