It depends on the exact version you have. Since I also have a 1998 C230 and I just worked on the brakes, I logged on to my AllData account to get the specifics for you. Once there I was reminded that there are the different versions. On mine (5/98 202.023) the front rotor thickness new is 12mm and service limit is 10 mm. On the rear it is 9 new and 7.3 service limit. My disks all have about 80,000 miles on them and the rear are still 8.9mm but the front are near 10mm so I will have to replace the front ones soon which I will do when the pads are due next year. My front rotors are currently on their second set of pads. Of course, brake component life span is highly variable, depending on your driving style, habits and conditions.

Mike