Chris:
Larry is spot on about the corrosion. That is why I free them annually and use some emery paper on the pins to keep things movable. The firebox bolts, I back of the nut to protect the threads and tap, not hammer on the nut to break them free. Front seldom has issues unlike the rear bolt that catches plenty of gunk from grilling. I think after awhile aluminum pins would wear down to the point that they would fail.