I've been using sickles for a while and have noticed that if I snag them and straighten the hook out and rebend back into shape 4-5 times they will break. As for lead being too hot I don't think so if anything that would remove some temper from the steel and make the hook softer. I remember as a youngun that some people would heat the hook up with a match to make it easyer to bend. My 2 cents worth anyway.