It can be replaced with 1/2" copper pipe. I mushed one once pulling the engine when it swung out of control, and my straightening efforts just split it. I used some pipe and one or two 90* bends to replace it. If it's the one that's made onto the heater core, I'd just cut it and splice with a piece of rubber hose and a couple of clamps. This is an opportunity to take the heater core out and flush it...

Not responsible for advice not taken...