I just got an "excellent" rated A12 back from KEH. When attached to the camera it has maybe a millimeter of rotational play in the plane of the mating surface. The film plane does not change, but how much play is too much? My other back moves a lot less. It's enough to feel it but not really see it, if that makes sense. With the new back, however, you can clearly see the movement. As the back seems otherwise perfectly clean I'm hesitant to send it back, but I'm guessing I should.