Following video shows how to upgrade your vive pro lenses with GearVR adaptor kit, but it shows how to replace the lenses. Hope it helps https://youtu.be/aPO0Dh7CMg4

The thing inside that holds the knob is plastic so there is little you can do to replace it unless you replace most of the back part, the only thing you can probably do is to get the deluxe strap for vive and replace all the back part of the headset

Seems that is a common issue with vive pro, headphones will start to fail eventually with use, good thing is that those can be replaced easily. A more permanent solution will be to use the Vive DAS (Deluxe Audio Strap) and replace all the back part of the headset, DAS has appeared to be way more sturdy and headphones can be connected to vive pro with USB C to headjack adaptor. You will also need a headset mount adaptor, this is available to 3D print for free on thingiverse

That happen to me recently, main suspect is sweat since I use it for excersice, since this site has already posted a tear down video I see the mic is located, the thing will be to actually get the part