Oh man, backstabbed aluminum... that's the trifecta of bad news. Did a whole condo rewire once and I'm still finding bits of old wire in my tool bag years later.
Used to think aluminum wiring was just a bit fussy until you had to work with it. Then I pulled a backstabbed outlet like @morgan.jason mentioned and the wire just crumbled in my hand. That was the moment I realized it wasn't just old, it was dangerous. Now I see aluminum and my first thought is a full rewire, no question. You find those brittle ends everywhere and it just proves the whole system is shot.