Any durable good - be they cars, reclining chairs, gun belts or what have you - that endures wear of some sort will eventually need replacing. When that happens depends on the good in question. That said, it should be replaced when it reaches the end or nears the end of its usable life.
Some goods last longer than others. A steel core gun belt is going to outlast one with no core. A Stickley Morris chair is probably going to outlast a La-Z-Boy. Not that there's anything wrong with them..