The brakes failed on my D2, 4.2, A8, LWB, recently. It would appear that the nearside caliper was sticking which caused the brake to overheat and after a spirited drive they failed. I managed to bring the car to a halt and had it transported home. Audi looked at the car and said the caliper needed replaced and quoted around £1600 for two new calipers, disks and pads. That seemed a bit steep so I ordered two exchange calipers. When they arrived they were incorrect. I then sent my original calipers to Godspeed Brakes who quoted me around £200 and 3 to 5 days to refurbish them. A month later they returned them to me and said they were unable to source the parts required to refurbish them. Finally I sent them to http
www.brake-caliper-painting.com. They quoted me around £200 including return shipping. Four days later my calipers were returned to me reconditioned and painted. I would recommend them and I wish I had found them sooner. Hope this helps someone.