Stepper motor Belt cog issue

[chbeckdb9]

Alright so after dealing with the motor wiring issue earlier today, naturally I wanted to get the thing printing. Everything was going well until I started doing axis travel calibration. The Y axis had a surging motion when traveling, particularly going down. A quick inspection revealed the black plastic gear cog the belt runs on is cracked, and the metal sleeve this is attached to, which is fastened to the motor shaft with hex head keepers is not on the motor shaft " square". For example it is like a wheel out of round, always having a "lump" on one side which jolts the belt and causes a rough motion. I can post another video, but I feel a few pictures will do it justice. Not sure what the best way to proceed to fix this is ?
Once again, Thank you so much for all the replies. I am amazed how helpful everyone is and extremely grateful for this!

[lordbinky]

Contact SeeMeCNC, I (and a couple others) had a couple like that and they sent replacements to me.