Those balers have a valve in the tongue that has a check valve and pressure relief valve that builds/holds the pressure on the bale. The door will be open a few inches when you are baling with them. That is the only way they will work.
Your leaking SCV will make the baler not work if it is putting any pressure on the lift side of the baler door. This will not allow the check valve to close and build pressure. A way to check the baler system is to close the door and hold the pressure on the close side until the pressure gauge is a high as your tractor will go. Then unhook the return line from your SCV. IF the baler makes a tight bale then your SCV valve is causing the trouble. IF the baler still does not build pressure then the check valve/pressure relief valve on the baler is not working.