Changing the rear brake sensor is easy. I recently put on new rear
brake pads and rotors on my 90 E34 535i, 5 spd, 104K miles, and forgot
to get a new brake sensor. Since the brake sensor warning stayed on,
the next day, I dropped by a local auto parts shop and purchased the
sensor for $6. I think jacked up the car, removed the rear wheel and
popped out the old sensor and plugged in the new. Done. Fast, easy and
cheap. What's not to like!