Barrel of the via? I’m unfamiliar with that terminology – what is that? I did a continuity check from the very bottom to the very top and everything tested good. When the audio is out, twisting the header a bit would usually bring it back so I assume(d) it was just a poor connection somewhere despite the continuity check.

Do you have a specific link? Is it aerosol (that’s what I’m finding)?

Do I just individually put a drop of that in each through hole basically? No cleanup, just let it rest in the hole?