The black wire on my part cooling fans have now both snapped off. I think the problem is that, while the white wire is nicely captured under a piece of plastic, the black wire floats free and thus whenever you make a change to the system has a chance to snap the very dainty soldering. After re-soldering it, I had the idea to use a piece of filament to jam into the hole. I don't think the black wire will come free again. I used a piece of green Edge filament, but you can use any 1.75mm colour you like if you feel like securing your wires in the same way.