Thin 1 pixel Intermittent Horizontal Line on Screen

The issue is not within the Display Cable (Retina systems don't use LVDS signaling, they use iDP or eDP). Yes, the early Retina models used the same connector system like the older Unibodies.

Anyways... your issue is within the ribbon cables between the LCD panel and the narrow T-CON board near the hinge side. The T-CON converts the iDP/eDP signals into what the LCD needs to power up the horizontal row and its corresponding vertical row so the intersecting Pixel is lit. Here the horizontal row connection is not holding fast either due to a misalignment and/or bad connection solder or clamp pressure. It can also be caused by a micro-fracture within the LCD panel so the pathway to the horizontal row point of the panel given row is not a viable path. We call this problem generically a TAB error.

To fix this might be as simple as adding some slight pressure across the ribbon solder joint on the LCD panel. Massaging or adding additional padding to press the area down. With solder joints passing a hot soldering iron across the ribbon to re-melt the joint might also work if you suspect a cold joint.