The control valve that uses a hand turn knob under the seat on my 650 is rusted and I cannot adjust the speed of the 3 point hitch. I have soaked it in PB blaster and used channel locks and finally got about 1 rotation of adjustment. I have tried cleaning the threads with a wire brush and putting grease on the threads and turning it back and forth to hopefully increase the travel but I have had no success. Any advise on a product that could help to loosen this? Or maybe I should go at this a different way?