Piston Cup on Glock 32

[hapi]

Hi Guys

I bought a KJW G32 and finally recieved mags to test only for it to vent the whole mag,stripped the slide and found that the valve sring and valve stopper are missing which is no a big problem but I can't figure out if the piston packing should be retained to the piston or not as the diagram I have is not to clear. Any advise would be welcome, Thanks.