[rotorwrench]

Corrosion has a way of welding parts together. Heating it and melting bees wax down in there might do the trick. Impacting it without beating it to death can sometimes get the corrosion in the threads to soften & break free but it takes a lot of patience to do these type of jobs. If it ever does break free, you may have to keep rotating it both directions to keep the threads from galling until it will rotate out without much torque applied.