OK so the only thing I can think of is that one of the capacitors that is attached to the negative end of the volume control pot might of went bad or were faulty, in the physical radio itself there are 2 capacitors that are going off of the volume control pot negative leg, which is weird because looking at the schematic there's only one capacitor coming off the Negative leg, which is C14 unless I'm missing something...
In the actual radio chassis, there's a mica capacitor that's going between the negative leg of the volume control pot and one of the taps on the volume control pot, which that mica capacitor isn't marked on the schematic (at least not that I can see of anyways) there's 2 capacitors marked on the schematic in that area that seem like they might fit the description of a mica capacitor value wise but the way they are drawn on the schematic they don't seem to connect from the tap of the volume control to the negative leg of the volume control pot, C12, which is a 350 pF capacitor is one possibility, the other is C9 which is a 25 pF capacitor, but like I said none of those capacitors appear to have a physical connection with the volume control pot negative lead and the tap on the schematic.