^ That. Or put the saddle on the floor (carpet) and brace one foot on it and pull on the stirrup leather. If you can get enough muscle on it, it should move. Then what I do is put a lot of Bick 4 on the stirrup leather and work it back and forth until it decided that it wants to slide. I'm not a huge Bick 4 fan, but it has some kind of wax in it that seems to reduce the friction so that the leathers slide more easily. They get stuck because people never move or change them. If the leather is drying out, that only makes them stick more resolutely.