Your problem is the sheath over the wire broke for whatever reason. It’s creating a stress riser and if that is not addressed it will wear out again. This is the reason why headphones and iphone cables always turtleneck, because that jack terminal is a stress riser. I don’t know if it’s intentional, or planned obsolescence. Your only real permanent fix is to take the entire motor apart, find where the cable terminates, and replace it with a brand new cable. I don’t know if this is even possible at all.
But in short, the metal sheath broke, and is cutting into the soft cable insulation. That metal sheath must be addressed somehow. Either removed, or patched up in such a way that it cannot flex at all. But wherever the cable go into the motor must be backed up with something soft, something NOT metal. Or else it will simply be cut by the metal.