Hi all My mechanic is telling me that he can't get replacement aux heater lines for my 2003 Yukon XL. Unfortunately one of mine wore through the metal line, where it had been rubbing against a flange near the rear of the vehicle. I'm floored that the part is simply not available, not made. This is my first GM vehicle in forever. It's less than 8 years old. Is parts availability that sketchy in general?