As someone who has broken (and seen broken) numerous Campy seat-binder bolts, I can state that the two primary causes are not adequately greasing the threads, and the screw bottoming-out in the sleeve. The latter happens when the binder on the frame is slightly undersized or "stretched", therefore not allowing for the length of the binder bolt, or the required washer is not used. Sometimes, all that's needed is a second washer as a spacer.
That said, Campy's binder bolts are not as robust as they should be. The bolt is weak, and almost always breaks at the same place, at the last thread below the crown. Anyone know of a source for a high quality, hardened stainless steel binder bolt assembly?
Falls Church VA