I have an older Case 1835C uniloader. It was working great for about 4 months. Then one day while moving some dirt the joysticks started feeling weak untill everything stopped responding. The fluid level is good. No leaks. The pump seams to work because when i start it up it will move forward and back for about 10 yards. Then give out. The bucket controls get no response. If i keep holding the joysticks forward or back, the machine will make a squeeling noise on and off and each time the machine squeals I'll jolt forward or back for a second. Can this be air in the system?