Good question, I bought the nismo exhaust with some miles on already and it must have been 2-3 years at least now, say, 20k miles on top of what it was when I got it, which I think was not that much, 15k?
May well have been the berk hfcs when I had them on hastened it a bit and no doubt these completely stupid and unnecessary one way traps which scraped them at a park and ride (at sod all mph, the right way).
I think ian swapped his for an ichiba and had no more issues, I may consider the same, depending on how long I want to keep the z.