The hard line(s) rarely, if ever fail. The rubber hose will, and I've seen guys grab a handy piece of rubber line and replace them. Problem is that most of the rubber line is not rated for high temperature oil. They fail and pump the trans fluid out in a very quick fashion. Make sure you use hose that is marked "TRANS COOLER". Braided lines are not a bad option, but again, make sure the lines are compatible with the intended use. There is a bucket full of different type hose, all very neatly wrapped in a stainless steel braid. You just can't tell if it's any good.