The lip seal on one of my Hydro Gear pumps is leaking and needs to be replaced. Do I need to drain the two gallon tank that is overhead or will leakage not be a big deal. It seems to be as simple as pulling the old seal out and pressing the new one in but I don't know if the control arm of the pump is under any kind of oil pressure from the sump or not. It is on an older Bunton Hydro. Thanks for any help.