I would bet that the reason the bolt broke is that soemone changed the original to a hardware store bolt. look at the head of the bolt (if you still have it).....there should be marks on the top......if there is nothing there, it's a cheapo soft bolt.

ALL brake hardware....cars/bikes/trucks should be a grade 5 or higher......

I would replace all the bolts on that stock setup with some hardened steel harware, adn wouldn't give it another thought....and yeah, some loktite wouldn't hurt...don't use the red stuff!!