Using those small "flea clip" type header pins for fan power never was a good idea to me. There is just too little guarantee that you will have adequate contact area between the male and female. As the contact area decreases, the remaining contact area gets hotter. The hotter it gets, the greater the loss and hence more heat. Once deterioration starts, it is on a vicious circle type spiral downward. I'm truly amazed more people don't report problems with this approach than I've seen. They sure are an "Achilles Heel" looking for an inopportune time to manifest. I realize the value of this approach when it coes time to replace a fan, versus having to solder and unsolder the wires, but you'd think there would be a better way to connect them. Perhaps a small terminal strip with screws, though they require a certain degree of motor skill.
73, Hoot