Most Predicta flybacks are presumed to be bad because
the outer insulation has flacked off. I have found very few actual bad ones. Sometimes the hv lead has broken away.You can usually find the end and resolder it to the flyback and then epoxy the metal clip it and the 1X2 lead attach to. Make sure you have continuity betwee the 1x2 lead and the 12 or 6BQ6 plate lead.When the epoxy is dry,remove as much of the old insulation on the coil as posible and coat the whole coil with black GE RTV.
The best way to test one is with a flyback tester which excites it and measures the Q of the flyback.