Brake Rotors
I'd buy a micrometer and measure the thickness of the rotors. Although to a lessor degree, like brake pads, rotors wear (they get thinner). Once they've worn to a certain point, they should be replaced when changing pads. That's because once they get past a certain thickness, they will warp. Micrometers are inexpensive and easy to use.
Mercedes-Benz advises that their rotors should not be turned. Porsche states the same thing. Turning them removes material. This makes them thinner than they already are.
....touch the rotors with your finger. Glide it across in every direction and feel if it's smooth. If there's grooves and any unevenness, you need to change rotors asap. If not, then it doesn't necessarily mean that you should keep 'em. It could be warped but not detectable by the dumb finger method. In either case, I highly recommend the meter as stated above.
THanks for the photo by the way. Your contribution helps.
New rotors aren't that expensive (especially blank ones) and turning the rotors will probably cost you $15-$20 each anyway.
Theoretically, new rotors are *supposed* to be turned to check for an even surface before installing, but this shouldn't be a problem if you're using high-quality OEM-replacement rotors (such as brembo blanks)







