I hate to say it, but I am feelings the aches & pains of aging myself.
You didn't list your equipment (separates or integrated, SS or tube, etc.) and this may be helpful to know.
But, I also hate to say this, I think you are going to have to unhook that "jumble" of cables, unjumble them, and start from scratch hooking them up and see if that right channel comes back.
I know that is not what you want to hear and hopefully some one will come up with something better for you.