This is the second time this cable has failed in this machine (Apple fixed it once for free). Seeing the FIVE right-angle bends the cable makes to get from the disk to the motherboard connector makes it clear why this part fails. Being able to buy this cable from iFixit and follow the step-by-step guide is GREAT--since Apple refuses to touch machines after they are five years old.
One hint for reassembly: first pin the cable down with the four screws, then attach the motherboard connection, then use something to temporarily hold the disk connector/cable out of the way, then pre-place the sensor/light cable against the case so you know where you want it to go, then cheat the paper glue cover off of the sensor/light cable as you smooth it against the case. Then the disk connector goes onto the disk, the disk seats easily, and then the retaining bracket is trivial.
Removing the sensor/light/disk-seat from the case was a little fiddly. It feels "stuck" because the cable is GLUED to the case!