JC120 chorus vibrato kills one speaker

[g1]

That is not really getting closer. One speaker should not work if chorus/vib is not working. So that was normal for chorus faults. Now you have just bypassed the switch.
You need to verify the switch operation with resistance measurements.
I would highly recommend against making any circuit changes til you fix the problem. At very least draw out how it was so you can change it back. I don't think anyone would have modified it to make the chorus/vib not work. That is what these amps are all about.
What does W11 connect?

[glebert]

It seems to me that you need to figure out where signal is present, and if the chorus/trem oscillator is working, to move further. If you have an oscilloscope that will make things much easier, otherwise you have to set up a sine wave input and probe through the circuit and compare AC voltages to the numbers on the schematic. I think Q9 and Q10 are responsible for the routing of the normal and modulated signals. Also, as I mentioned before, make sure the oscillator is running, if not not getting an output from that side makes sense.