I can 100% confirm that I haven't touched any of them. If the radio had been opened before I bought it, it was well hidden as I had to slit the label down one side to open the case.I wouldn't be surprised. I suspect something like that. Perhaps not by the present owner, the TS.
With the above tests we can check out the audio section and maybe more.
Is there a need to split the audio from the source into two channels like your cable does or will a stereo cable suffice? I have a splitter but it would require some digging to find.