Seems like shower repair month for me--I have another shower valve question. I am trying to remove the stop valves (part 10 highlighted in the picture) from a grohmix valve with poor flow so I can clean the strainers. The valves are a brass nut/flange piece threaded into the brass valve body. I tried to unscrew both of them with a socket ratchet and they aren't budging. I am afraid of breaking the valve body or copper pipes with more force because I have no obvious way to apply a counter-force. I already removed the thermo cartridge and cleaned its strainer, but that didn't help. I actually think I made the poor flow problem worse by exercising the service stops to flush the valve body when the cartridge was out. Should I use an air impact wrench to back these out or is that a terrible idea? I used the air impact successfully on my water heater anode, but that was steel on steel and a much more massive assembly.