My panniers rubbing an aluminum rack wore about a third of the way through a strut in some 5-6 years' of commuting.
Since I'm saving two tanks of gas every month commuting by bike, I spent the money and replaced that rack with a Tubus rack. That was eight or ten years ago. My rack now has a bit of surface rust. At the rate it's deteriorating, I figure my grandson can inherit the rack when I retire, and use it should he decide to bicycle commute. He might want to replace it before he does a cross-country trip after he retires. Or he might decide to carry less than 50 pounds on the rear rack on that trip...