The controls on my truck look exactly like that GK-1. I even pulled the one apart, but it didn't appear that anything was serviceable inside. After seeing their construction, I would rather use a different type of valve to control them(one that actually has seals in it).
Are the 1/4" ball valves that Lowes have brass? Home Depot has 1/4" ball valves but they are plastic(and cheap looking).
I don't see why you can't put it to the "park" position, and then shut the ball valve off.