As you know the left earphone audio issue is well documented. Firstly ensure that the screw holding the left earphone to the headstrap is screwed in fully.
Next, if you can get the the audio to work with the headstrap in a certain position you can tape the strap to hold it in that position. See Link -
https://www.reddit.com/r/oculus/comments/dxz1cz/psa_rift_cv1_longevity_tips_for_both_ribbon_and/?rdt=40327
The constant movement of the ribbon cable as the headstrap adjusts to the size of your head has caused it to fail. The point of flex is within the headset body and not in the headstrap. If you're lucky it may only be the common ground to the left earphone that has failed, so slaving the ground connection to the right earphone ground may fix the problem, as seen in the first video. If the traces are damaged to the positive leaft earphone side then you'll have to do a similar mod but you'll only get mono audio.
How To Fix The Oculus Rift Left Audio Fault - YouTube
If these mods don't work, many folks just remove the headphones and have wired headphones going to the PC audio output.
This is a video of the actual ribbon cable fix which is fine work -
https://www.youtube.com/watch?v=Y7lo8hMwYNc
The original developer did mention that there would be a repair kit, but this never materialised. It's unlikely that meta support will be able to help as the headset is way out of warranty. Having said all that , the Rift CV1 is still a great and comfortable headset.