stepper motor is not working right need help finding replacement

i have a printrbot simple 2014 the y axes has stopped working properly it jerks i have switched the x axes with it just to be sure but it still does not step right its an kysan1124103 its 42mm wide and 42mm tall and 32mm deep with a 5mm shaft but i don't know the voltage or the amps and when i search it i can't find anything this stepper
looks like it would work it's 12v and .4 amps seem to be the same size what do you guys think... thank you
http://www.ebay.com/itm/Stepper-moto...D161071121692#

... you can find the reference on the picture here :
http://printrbot.com/shop/large-kysan-motor/