I have a 4530 4wd T2. Today when I tried using the tractor, the box blade wouldn't lift. When turning off the ignition the blade immediately raised about 3 inches. In order to get it fully raised, I had to turn the tractor on and off. It lowers fine and all other hydraulic functions work. The fluid is also fine. I fiddled with the control knob below the seat but that did not have any effect. Any ideas before I try to open this baby up?