Need Help with Umarex Fusion 2 Disassembly to Fix Leak

I believe I need to take this apart further to clean or rebuild the poppet and/or other parts still in this 'receiver'. Any pointers on how to get the remaining parts out?

And, fwiw, I'm dealing with a persistent leak out the barrel that drains the CO2 cylinders down within minutes. I hear a hiss after firing. Blowing the parts off with compressed air fixed the issue for a few dozen shots, but the problem is back with a vengeance.



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The photo below shows the rear view.
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The photo below shows the front view.
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