Umarex Huben Dream valve notos air leak. How to dissemble?

Got a Huben dream-notos reg (yes, it is a real one). But it has a leak where the plenum and the gun meet, sort of. There is this metal band of sorts that the plenum goes into and that goes into the gun. Hard to explain, just look at the image. The red circle is where it is leaking.

I'm guessing there is an o-ring in there that is messed up or perhaps it just needs tightened. Problem is I'm not sure how to take that part off. You can see in the picture that there is a hole there but there isn't a screw or anything there, just a hole.
My guess is you stick something in there and just turn it. But before I do that I wanted to ask before I do something that could mess it up.
dream-notos_reg.png
 
That part will unscrew.
There is a 8mm Hex inside the plenum to remove the whole plenum.
The part you circles is the threading & attachment difference between the Notos and the Universal.
I had issues with the very first Universal the o'ring channel abobe the threads was wrong and the oring would blow out.
Email Nick Scott <[email protected]> with your issue and they usually are quite helpful.

-- Matt
 
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Thanks for the reply
That part will unscrew.
There is a 8mm Hex inside the plenum to remove the whole plenum.
The part you circles is the threading & attachment difference between the Notos and the Universal.
I had issues with the very first Universal the o'ring channel abobe the threads was wrong and the oring would blow out.
Email Nick Scott <[email protected]> with your issue and they usually are quite helpful.

-- Matt

Thanks for the reply. I got it off with some effort, it was really tight on there. I replaced the o-ring and it seems to be holding air now. I did contact Nick he was helpful and responded faster then I expected.