One problem related to brake pedal and linkage has been reported for the 1998 Audi A6. The most recently reported issues are listed below.
After slowing for a left turn from main thoroughfare to side street, my brake pedalfailed to depress to slow the car down. I had to allow the car to coast to a slower speed and then to a stop. After clearing snow from the wheel wells and allowing the car to sit with the engine off for approximately 20 minutes, the brake pedal "unlocked" and I was able to depress the pedal once more.