i installed some brembo blanks at all 4 corners a couple months ago, today when i went to install some new rims i noticed little cracks on the rotor by where the 2 screw hold the rotor on to the hub. i did not use these screw to hold the rotor on because i was told the lugs do the job and the screws are not nessecary. it is only on the one side front and back. the cracks are very little in depth and size but you finger nail does it caught on the crack, so i was wondering what could cause this and is it unsafe to still use these