Cast iron rusts, there will be surface rust on even new rotors after a few days. Now, if the rotors are severely warped and causing the shddering, then they should be replaced. Above poster made a good point about a primary cause of rotor warping, putting the lug bolts on too tight. Is anything actually worn, or is the complaint just shuddering upon braking?

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record