Spray some Breakfree CLP into the gas relief hole and angle the rifle barrel down in a gun vise or makeshift rig so the CLP works it way into the gas plug threads. Let the CLP work for 24-48 hrs, then use the GI universal tool on the nut along with the barrel/gas tube wrench. You should be able to break the gas tube nut by squeezing both tools together. Clean the gas tube using a bore cleaner and a brass brush and spray down the piston with brake cleaner to remove the CLP. Then lightly apply a light coating of anti-seize to the threads of the gas plug for future removal.