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I wonder if you have one or more funky sockets on the boards. That is suggested by an old jumper to a socket pin. Sometimes resoldering pin connections on the sockets can help. Obviously, you want to be delicate with any work on those boards, to avoid lifting traces, etc.
I am curious how you fixed the vertical problem. Intermittency (fixed by wiggling tubes) also suggests bad socket-to-board connections, or simply a bad socket.
Sometimes you can improve sockets by cleaning the devil out of them or (carefully!) bending the metal inside the socket holes to make better connections.
Phil Nelson
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