I have a GE JGP389WEVWW cooktop that was given to me. The manifold had been take out and the valves had been disassembled. I found enough parts to reassemble 1 valve. The actual valves are intact. What is missing is the stems, springs and othe parts that actually turn the valve within the valve block. Are these parts available? If I have to purchase new valves, how do you know which valves go where? I noticed that there are 2 different parts(ap2023686 and ap2023687) for this model.