I am interested to learn more about this as well. My ABS light has been on for such a long time and I've learned to ignore it. The light will turn off sometimes and the following day it will be on again.
Many have suggested replacing the brake light switch at the bottom of the dash, which I've done 2x. I've also replaced
the speed sensor but the problem persists.
My C230's brake system (Rotors, disc brake pad, brake sensor) was serviced 5000 miles ago using only OEM parts by yours truly.