Robert Kaufmann wanted suggestions regarding Campagnolo cranks and breakage.
First be sure that your foot and or strap has not burnished a polish or as sometimes seen worn away a portion of the crank arm. If so, move your toe clip outboard to clear, can be difficult and may require cleat adjustment. I have seen many cranks that failed after they had been "polished". Most of the arms also showed a dirty area at the break indicating a prior crack that compromised the strength of the arm, well before failure.
One has to look, found a Cinelli stem with a crack recently.
Buying a used crank? Polished regions on the arms from feet or ankles need not be considered in my book.
John Jorgensen
Torrance Ca