OK, so a little update, it was definitely the original speaker that was bad (bad humbucking coil) because I installed the speaker from the parts radio like this one, and it for sure was not humming whereas the original speaker that came with this radio did hum, in fact when I looked at the parts radio speaker and the original speaker for this radio, it actually looks like the original speaker was maybe missing its humbucking coil (it only had two wires coming out of the field coil whereas the parts speaker had 4 wires coming out of the field coil.)
So now I can officially say that this radio is fixed, unfortunately though the parts radio's speaker was slightly smaller than the original speaker was, so I had to modify it slightly to make it fit in the cabinet.
