I just had to replace #5 injector line due to it breaking of at the head. Something that surprised me is that it would appear that the injector line appears to to be double walled with a very small line inside of the outer line separated by what appears to be nylon. I don't know that be an absolute fact but this is what I see from the damaged parts. Here is a pic of the knob that broke off at the head.
I have not been able to cut the old line open to see. Is the entire line of this same construction? If so that would explain why I could not fold the line over to crimp it off. I will cut the old line open tomorrow and see what is there.