One source part number 103623-004 Accumulator charging tool (kit). You will have to get a gas cyl from a local gas supplier. Just follow instructions exactly when recharging. Its actually pretty easy.

Slowly open the plug on the accumulator, and be ready to screw it back in quickly. If you hear a hiss, it is probably OK, as it should have nitrogen in it. If oil comes out, replace it. The accumulator is bad. It needs to be charged by the dealer to either 350 PSI or 500 PSI of nitrogen.. I don't remember the spec for sure.

MOST crown hydraulic cylinders have an air bleed screw towards the top of the cylinder crack it open and bleed any air that may be in the system.

a couple of questions come to mind about this issue...
- does it do this while the carriage or mast is moving or when you release the lever/handle to stop movement, (when movement is stopped the mast/carriage bounces) ???

- have you checked the mast and/or carriage to see if there is anything restricting movement, does it do this in one particular spot or at any position? are there any abnormal noises when this happens?

although it does sound like an accumulator issue i would rule out any other possible problem before replacing any parts.

generally when you get a bounce when movement is stopped (if thats what this is doing) it is due to air in the line(s) or in the accumulator.
If there is a bleeder screw on the hydraulic side try and bleed out the air, if no bleeder just crack the line with the forks slightly elevated and let it bleed out for a sec, if there is air it should come out then.
IF you do get air i would look for where it is getting the air from.

If i can think of anything else i'll come back and post it, but to me it just sounds like air in the system.

I thought that also, should I replace it or have it recharged?

Sounds like bad accumulator maybe