If all of your voltages look good, my first guess would be damaged OT.
It is possible for an output transformer to be damaged in such a way that it will result in the symptom you describe. Given that you witnessed a catastrophic failure of one of the OT primary leads, I'd say the chances are even better.
I don't know what equipment you have available, but you can test the turns ratio of a transformer fairly easily by applying 6.5VAC to the primary and measuring the AC voltage on the secondary.
I would first disconnect it from the circuit and measure the DC resistances between the primary leads and the center tap. If they are way different, you know something is wrong.