I've recently run into issues with things like outlets not providing any power, seats not reclining even when they definitely should, etc. Obviously they can't fix it during the flight, so it seems like pointless whining to bring it up. I would like their maintenance crew to know it's broken, so they can fix it the next time they get a chance, but I'm not sure the best way to inform them. Maybe they do regular inspections for that sort of thing, and they wouldn't be able to fix it sooner regardless of what I do. I'm hesitant to inform the flight attendants, because I don't want them to think I'm obnoxious, and I have no idea if this is part of their responsibilities or not.
If there is a non-urgent problem with the plane that cannot be addressed in-flight, who should I notify, if anyone?