[Arran]

Peter;
I can't say for certain but many North American made radios from that era, the late 1940s onward, had silver mica capacitors inside the permeable tuned IF transformers, that would fail over time. There were two ways that they could fail, both related to the way they were constructed, one was silver migration, as you can see in the thread Ed posted about the Zenith H-725 AM/FM set, the other issues was a poor or intermittent connection between the silver layered "plates" and the the coils. It was not a very good way to construct these since silver tarnishes if exposed to the air, and can also migrate to the other side since there is a high DC voltage potential between the two plates. I was thinking that this may be a cause for the poor performance of your Hallicrafters, the selenium rectifiers can also become tired resulting in low B+ voltage, and poor performance as well.
Hallicrafters, being a manufacturer of communications receivers, designed, and marketed a number of multi band portables, such as the TW-500, TW-1000, and TW-2000. I do not own any of these models but I have a Sears Silvertone portable that I suspect may have been built for Sears and Roebuck by Hallicrafters as it also uses a turret style bandswitch with the mixer-oscillator and RF amplifier tubes mounted on top like a TV tuner.
Regards
Arran