My independent MB mechanic just purchased another piece of diagnostic equipment which monitors all of the circuits in the car while rolling. Finally, he was able to isolate my ABS problem to the driver's side ABS sensor. He replaced it last night, and so far, no more ABS light. I am planning on bringing the car back in to have him run through all of the systems, since I still have a very intermittent, very strange idle problem which thus far has gone undiagnosed.