Unanswered which stepper in Robo 3d

One of the stepper in my Robo 3d printer is binding.. I looked for the specs on that from Robo but didn;t see it.

Here's what I think I need:

Nema 17 size
5mm shaft with machined flat
200 steps per revolution
12v (there are lots of nema 17's with other voltages)
Holding torque ( in/oz) there is a wide range for these, what does the Robo have/need?

I am assuming that all 5 steppers in this machine are the same, but just in case, it's a z-axis motor.

 

Are you sure it is the motor and not just the driver?