found a bad bearing when i did my rotors last weekend. must be a material defect of some sort, all 4 were changed 30,000 miles ago and this one is the only bad one. hard to see but has pitted rollers. race didnt look damged at all. had no noise or vibration, i was pretty shocked to have found it. the weird thing of it is that back 4 years ago when i put new bearings in was because of a bad bearing in the same position, drivers side inner. that time it was the race that looked bad, almost like it had sat with water in it, you could see where each roller was in the race. i still have that race but the picture i have for it doesnt show up very well, this one aint great either but at least its somewhat veiwable.

 

I assume that when you changed out this bad bearing you also replaced the race . If you change one you have to change the other , even if it looks OK.
That pic looks as though there was some grit running around in the bearing .

 

the new rotors came with new races already installed, yes i would have changed out the race if i was useing the old rotors, the grease looked clean, no sign of water/dirt intruding.