All:
In total, I received reports of 16 crank arms that were personally broken by a total of 10 CR list members. The most one person broke was four. Many broke two (sometimes the left and right of the same pair, months or even years apart).
Brands that were reported broken were:
Avocet (Ofmega) Campagnolo Shimano Stronglight Zeus
With the exception of the Shimano arm, 100% of the arms broke at or near the pedal eye. The Shimano arm broke mid-way between the pedal eye and the spindle hole, and looked like a casting void issue, per the reporting rider. Zero of them broke at or near the infamous "spider crack" area. Not a one!
15 of the 16 arms were right-hand ones. Darn near 100%. The only left-hand one that failed had "50,000+ miles" on it at the time of failure.
Average estimated mileage on the crank arms at time of failure was about 20,000.
Of the ten people that broke crank arms, eight broke multiple other bike parts, including a Concor saddle, a Cinelli 1R stem, a Cinelli pedal, steel frames, aluminum frames, block chains, roller chains, freewheels, BB spindles, hub flanges, rims, handlebars, and spokes.
What can we take away from this? Well, it's small sample size, but it says that about 0.1% of the current CR list members have personally broken a crank arm. The most surprising thing to me was the amazing consistency of the failure points on the arms - left or right, Campy or Stronglight or whatever, low or high-mileage, they all failed at essentially the same spot!
Check those high-mileage right-hand vintage arms for cracks near the pedal eyes, I guess.....
Greg "cranked to the max." Parker
Ann Arbor, Michigan