Replacing selenium rectifiers with silicon diode or maybe a bridge rectifier. Some AM-FM hot chassis sets use many tubes, too many to string in a 35W4 tube rectifier. So a selenium rectifier was used. Like wax capacitors, these will fail in time. Best replace the function with a silicon diode like a 1N4007.
Electrolytics can take a temporary overstress for a short while, like heater warm up time.
It doesn't matter which end of the selenium rectifier serves as the tie point. Check to be sure there are no leakage paths to the chassis. The mid point of the heater string will look to have minimal AC waveform in reference to the B- line of the bridge rectifier. This is fine, cathodes like their heaters to have a positive bias. Disconnect the heater line of the other audio output heater pin.