The brake valve is an easy rebuild, but are you sure that is the problem? Have you tried capping the line off to the right side? If pedal still goes to floor with line capped off, then problem is with the valve. If pedal is hard, then problem is in brake piston in axle housing. Also, what happens if you push both pedals together? If pedals are hard when pushed together, may only need to adjust pedal stop screws. Back out screws until they contact pedals and then 1/3 turn more. If one pedal is higher than other, turn that screw out 1/6 turn more.