Replacing burner gas valve on Jenn-air range JDS9860AAP

I have a gas burner valve that I cannot turn off (due to the valve stem being stripped) and need to replace it. The service manual tells me I need to replace the manifold and the valve. Can someone enlighten me as to why the manifold must be replaced? Also does this mean all four burner valves will need to be replaced when the manifold is replaced?

Item I need to replace is #9 in the attached assembly drawing.