ulysses, my Oleopnuematic expert buddy, I have a question for you on the rebuild and also an idea how to remove the stupid rear air valve:
1st picture, is the muzzle end of the barrel, you can see moderate corrosion here. I guess from the gun being -12m for 2 months

I have cleaned the internal chamfer, but can do little for the threads. I have no access to parts yet, so will rebuild as is. Do you see any problems?
2. picture. The asso air valve has a wide slot, that in my case was very very tight. In the videos a small simple and narrow metal key is shown. I think the asso valve is different. I made this tool from a 15mm socket, ground down and used with the 1/2" socket handle. It was very very tight, but moved on the 10th attempt.
Cheers!