Am I seeing a dark coloration in one corner of the broken surface? (bottom right in the first pic). If yes, then the arm had cracked quite a while ago and the material corroded until the crack got too big... Pretty damn nasty. I just hope to God my $15 cranks (and that's MSRP!!!) won't do that to me. I'm glad you got out of it unharmed, and now you have a cool paperweight you can show off.