You can make the brass tube if you want. I'm installing a new serpentine evaporator and found that the brass tube in the original evaporator, was cracked. I used a beveled punch to flare the end of a ~ 5" piece of new brass tube, pinched the other end and cut to the length I needed...works perfect. In the pics below you can see the original tube is about 4 3/4" +/- long (the new one I made is a little shorter because of the way it needs to fit in the serpentine evaporator).
another thought...it could be that the flare collapsed or cracked on the end of your brass tube, allowing it to slide down into the evaporator housing.
