I'm by no means an expert on this, but I can tell you my experience. I bought my c5 in late May of this year, did the 300 mile oil change about 10 days later, and then I changed the oil again at 1200 miles because I'm overly cautious. Anyway, when i changed the oil at 1200, i can tell you i still found quite a bit of the metal flakes on both of the magnets, significantly less than at the first oil change, but enough to where if i were you, I wouldn't want that floating around in my oil.