Does anybody have experience replacing the line on the left in the images below that are connected to the arm. I've tried wrenching underneath but it's very tight. Any suggestions? Thanks
Air hammer is your friend here. An sds hammer drill on hammer only would also help. Just hit on the flats of the fitting for a bit and it should loosen right up. In a real pinch, if I am sure to be replacing the fitting, such as in your case with a hose, I will take a sharp chisel bit and hit on the corner of the hex on the offending fitting to get it turning. I call it the linear wrench method.