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A good option for stuck filters: RELAX.
Sometimes one of my filters got stuck, to the point that I finally desisted removing it. However, a few minutes or hours later, it could easily go out at the first try. This was very frecuent, so I got used to it, and at the same time a bit surprised.
I think that this is the reason: when it is difficult to remove a filter, usually one applies even more pressure with your fingers, and it becomes even more difficult to turn it. You get nervous, angry, and press even more.... this is the no return point. As much in a hurry you are, it will get more stuck.
However, sliding the fingers with a very *soft* pressure, chances are that that it will turn. I think that applying too much force may deform the filter or adaptor ring (including the tough B+W Kasemanns) making it slightly elliptical and less prone to turn. Ok, force is necessary... just that perhaps the minimum to avoid slipping the fingers...