This is a very common problem with these units. You can easily fix this by spraying the brake pivot shaft with some penetrating oil and instead of rotating the shaft work it in and out. A free shaft will move about half and inch or so. I use a pry bar and a small hammer. Start by taping the shaft in and use a prybar to get under the lip of the bracket and pull it out. These are tough arms but dont get to crazy with the hammer and pry bar. Keep doing this and spraying oil, within a few minutes the shaft will free up and rotate correctly. I then use fluid film to spray a final lube on the shaft..
Never had to remove a brake shaft to free up... hope this helps!