Do they need to be replaced or is there some can I can spray on to tough to turn old shut off valves ..like wd40[or is that corrosive?]Also .I am adding a bypass to heater and updating some of the plumbing and noticed the overflow outlet on top of scimmer goes to waste outlet from sand filter and out to the street. There is a shut off valve from scimmer overflow line to that waste line from filter and another on the filter waste line out. Should I remove these or? What's the point of having shut offs when the overflow allows needs to remain on?