I can't even believe this worked, so I have to share it.
I have a pair of Jabra Elite Actrive 65t Earbuds, which I bought (renewed) almost three years ago. They are great headphones; good quality audio (in both directions, for calls), decent battery life, and small enough to keep in a pocket.
About six months ago, though, the left earbud started to fail. Sometimes, it would work well out of the charger pod, but within a minute its volume would fade to almost nothing. In a very quiet space, I could hear just the lowest bit of sound from it, but not useful at all.
I searched all over for a solution, tried re-pairing them, tried a different phone to pair with, etc. but nothing worked.
Then I stumbled across a post, which I've now lost, that said you can fix this problem by probing the tiny little hole on the inside (the "head" side) of the earbud to restore it. With nothing to lose, I tried it with a very sharp metal scraper, and it absolutely worked!
In the bottom of that little hole, I felt resistance - maybe a plastic or metal 'bottom' in the hole, so I just scraped around carefully for a couple seconds. I didn't see anything come out of there, nor did it look like it was plugged to start with. But the earbuds are both working great, again!