The spanner wrench from Harbor freight doesn't work.
The top hat valve is in the way, so there is no way to get the prongs into the small holes in the brass part under the valve.
I spent weeks buying different tools to try to get the valve out and then back in.
A local fabricating shop was finally able to get the brass part out, but once we put the o ring on it, it was impossible to get it to screw back into the bottle securely.
A post above recommended removing the entire valve assembly from the bottle, then work backwards to get access to the brass part without the top hat valve in the way.
Unfortunately, I was unable to get the collar off the bottle, although I was able to snap two drill bits trying.
The local shop was also unable to get the valve collar off. We used increasing force and larger tools, until the entire assembly was destroyed, both the neck, the valve, the brass part and the top hat were shredded clumps of twisted metal, all useless.
I spent several hundred dollars on tools and labor to try to get a 10 cent O ring replaced, and was never able to accomplish it.
I concluded that the Air force valve is an INCREDIBLY bad design. I learned my lesson, and will never purchase another Air force product.
I'm left with a useless air rifle, a great deal of lost time and money, and a firm resolve to do better research before investing heavily into a product that is so poorly designed.
My bad.