R3m disassembly write-up?

Ok, I’ve watched a few vids nd had my r3m mostly parts. However, all the vids I watched were single shot and did not show how the part at the breach end of the barrel comes of. This is the Oring and brass insert housing. Is this peice screwed to the barell assembly somehow and requires you to break the barrel loose? I don’t guess I need to remove it but I’d like to b able to remove this part from the barell without removing the barrel assembly from the air tube. I’m going to replace the breach Oring and I’d rather pull the brass insert than dig around with a pick but you can’t get to the set screw while its attached to the air tube. I see that the receiver has a hole in it so you can get to the set screw when the receiver is up against barrel, but I’m not sure why that is useful if it can’t be accessed when the airtube is in place. I don’t have a good way to hold the barrel while breaking barrel nut loose so I’m not trying any of that rite now. Also, I’ve always had issue with reusing sealing washers and stuff like that. I’m not real happy with the idea that the sealing device used to seal the valve body to transfer port is a brass sealing washer that I’ve been told is life of the unit. Does that mean its somehow attached to the valve body and can’t be repalced? I didn’t want to try to hard to remove it so I guess I don’t realy know that its permanently installed on the valve body. If replaceable, can anyone tell me if this is a common part used I other industry or some special sized part that has to b ordered from edgun? I’ve seen similar washers used on motorcycle break lines, but not this size. I’m assuming its common, but I dnt know where to look. I knew tht 6×1.5 orings are used somewhere on Honda auto and motorcycle, so it wasn’t hard to source it, but I’m not sure about this.