I was once (like ten years ago) on a transpacific flight with Northwest from KIX/RJBB to KDTW on a Boeing 747 and our flight as delayed at the gate for about an hour because of some issue with a "floating horizon" (I remembered incorrectly, the issue was a "artificial horizon").
Is that a malfunction with the attitude indicator? What exactly went wrong? It sounded like they fixed it by swapping out a component, maybe the instrument itself?