So I got an old HA from my saved avatars but it has no nose or mouth, i tried to change it but the basic noses and mouths don't seem to be clickable. Is it just me? Is there a trick? Or is just completely broken?

it's not working for me either, and yes just clicking on the choice you want should apply it and once applied then Save Avatar keeps it.

I don't see any threads in Problems & Bugs though. Maybe this is working for other people?

Double check that they aren't layered behind your base! You could be changing them by clicking but not seeing it because they are hidden from view.

when you load a saved/shared avatar, all the facial features disappear unfortunately. if you load it and click "save" and then refresh the page, they should reappear and then you can change and layer them as you like.