Yes. Had a bad solder joint inside the RCA of one interconnect. Very hard to find as it worked fine for so many years, then gradually progressively acting up. Seemed from the beginning to be a connection issue, but exactly where? Intermittent faults are the worst. You get there but slowly. Eventually narrowed it down to inside the plug, and still wasn't sure (just seemed so unlikely!) until taking it apart the wire just pulled right off! Re-soldered, and no problems since.
Yours sounded from the start like another contact problem. In your case parts expand as they heat up, eventually reaching a point where they lose contact. It could be like mine where its inside the IC, where the wires solder to the pins. Or it could be the RCA connection itself. Even a tiny amount of play could be enough for the IC to wiggle just enough for the signal pin, the part that sticks out, to lose contact with the clip, which is inside where you can't see it.
Not saying its either one, only saying now its narrowed down to a smaller area you have to really zoom in on every little thing going on in that area.
Yours sounded from the start like another contact problem. In your case parts expand as they heat up, eventually reaching a point where they lose contact. It could be like mine where its inside the IC, where the wires solder to the pins. Or it could be the RCA connection itself. Even a tiny amount of play could be enough for the IC to wiggle just enough for the signal pin, the part that sticks out, to lose contact with the clip, which is inside where you can't see it.
Not saying its either one, only saying now its narrowed down to a smaller area you have to really zoom in on every little thing going on in that area.