I just broke a motor too.
I had trashed the first set of blades after many contact with walls and furniture, so changed to the spare set. After about the fourth flight one blade of one prop snapped off at the root.
I foolishly span up the X4 with the half-prop. The vibration was able to spin the motor in the housing and twist up the wires. one wire snapped, and on removing the motor the other wire pulled out right where it enters the motor base.
90 minutes of micro-surgery later I sort-of had the motor running again but there was no way it could ever be relied upon.
Have ordered new props and motors but luckily I have 2 more X4s 'in stock' due to getting 3 for 2 at Modelzone. Though the third is a gift to someone else (probably!)
I'm wondering whether a dab of hot melt glue on the motor to housing interface would be strong enough to prevent the motor body spinning in the case. Cyano would be too brittle. Evo-Stik perhaps? Sticky, but easy to remove.