That's got to be it. The core tubes are getting fatigued through vibration. The odds of all these radiators across multiple brands being bad just can't be it. The common denominator is that fan.
First thing I would do is yank it out and power it up. If the balance is off you'll know it. Either way, stay away from those zip ties.
I'm using a Ford OEM fan from a V6 Contour on mine that is mounted to the frame of the radiator. Been in the car for 11 years with the same radiator.
