What do I really need? What is broken in my headset?

@alex70368 "if I press a little with my finger on the speaker arm the audio returns" is most likely a contact issue. Post some images of what yours look like. Use this guide Valve Index Headset Left Speaker Replacement for the removal. Then check the pins on your speaker. Make sure they have the same length and make sure there is no corrosion, debris or other obstruction etc. Also check the contacts in the headphone. Take some well focused images of this and post those with your Question. That way we can see what you see.

Hopefully you will not have to replace anything but if you do, it better just be the Left speaker. Anything else will be pretty involved. Valve Index Headset Left Speaker

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@alex70368 I am actually agreeing with you. It is not the speaker but I do believe that it is the contacts. I do believe that they are either not reaching anymore or have some other issues. Those two pins make contact with the contacts in the headphone. As you tighten the speaker to the body, they need to connect with those contacts. That is the part that I believe is not happening based on this "press a little with my finger on the speaker arm the audio returns to normal " Now, check those contacts on the speaker side. Do they feel like there is a spring that pushes the contact out (which is suspect)?

Try this, but only if you are up to it. It will not harm your speaker. Take some aluminium foil and fold it over a couple of times until you have the thickness of only a few millimeters. Make two of those slightly smaller in size than the size of the opening for the contacts shown in step 2 picture 2 of the guide I mentioned above. One piece of aluminium for each contact. Now reattach your speaker. Not to tight but tight enough that you know it makes contact. Then try and see if it works. If done right you should now get the sound back. Let me know if this makes sense. I don't want to bore you with any technobabble :-)