Cracked case, shutter button broken, USB port no longer charges the camera or gives video out for my FPV, wifi will not turn on, and it's stuck in 4K mode.
As Calvin said, I'd check with Gopro as well. They offered me 40% off a new hero 4 black when I called about my cracked lens. Was able to fix it for 50 bucks so I declined the deal, but they offered it up right away.
I've not come across a company fixing buttons/internals, though I imagine they are out there.