I would bet a few bucks that the small line in the web shown in the photo is the beginning of a crack , as a youngster hanging out at the American Cyclery, that was one of the many things I learned about . Oscar would knock the edge off the stress riser with a small jewelers file to prevent cracks from beginning and file through the cracks to stop them from spreading .
The sad thing is that the premier equipment manufacturer in the world , at that time , would let a part out with such an obvious flaw ,
I think the ones that are the most dangerous are the ones you don't see down around the pedal area . When mine broke it was obvious that it had been cracked for some time and was slowly working its way through the arm , the crash was spectacular .
The last arms I have purchased have been dye penetrant tested before I use them , its not as fool proof as Xray but a lot less expensive .
Jim McCoin
Fremont Ca.