Power Assist Brake problems of the 2001 Audi A4

12/2004, purchased certified 2001 Audi A4 from beechmont Audi in cincinnati, ohio. Car had a comprehensive 300+ point inspection performed by Audi as per paperwork. 5/20/2001, vehicle taken to bluegrass Audi in louisville, kentucky for a brake assist problem. Several days prior to brining the vehicle in, I was in reverse leaving my garage when I found that I needed to push the brake pedal to the floor to slow and stop the vehicle. I noticed when I drove forward the problem went away. I tried backing up again and found the braking to be normal. Later that afternoon I was going to lunch and when I backed up the vehicle didn't have any brake assist again and I had to push on the brake pedal with maximum force. Took the vehicle to my local Audi dealership and was told by the service manager that the car needed a brake flush. They performed the brake flush, but that didn't fix the problem. I returned the vehicle back to Audi several days later and was informed that they found the problem with a grommet that connects two vacuum hoses at the bulkhead. They added a clamp to stop the air from escaping the system, but the next day it proved not to work. They also informed me that the brake pads and rotors were within Audi limits. Took the vehicle back and was informed that they needed to replace the grommet. After the item was replaced, it still has the same problem as of 7/4/2005. In summary, the vehicle has a brake assist problem in reverse after the vehicle has been sitting for a short period of time. In my un-scientific research, the brake assist fails if the vehicle has been sitting and not running for less than 2-3 hours. When this occurs, the brakes operate, but maximum brake pressure is required to stop the vehicle until the pressure builds up. This could be an isolated incident, but I thought I would pass this information along just in case there are others with the same problem.