Brake Master Cylinder problems of the 2003 Volkswagen Passat

I bought my 2003 vw Passat wagon brand new. In a span of 3 years I have had to replace my rear rotors and brakes 4 times and have yet to replace the front rotors and brakes and the car is at 77,510. I had the left rear rotor replaced Jan. 21, 2004, the right rotor April 1, 2004, both left and right rotor Nov. 23, 2004, and then both again July 11, 2005. I was very concerned about this from the beginning and stressed the recurring issue with vw corporate since my warranty was running out and the problem was still persisting. When it happened again at my regular check up in June of 2005, after only 7 months and 11,427 miles from the last time I changed the brakes and rotors, I raised some red flags and suggested that I lemon law the car, vw researched and found that "there was excessive heat on my rear brakes and that my booster rod was bent and not releasing rear brake pressure completely". On July 11, 2005 vw replaced the brake booster, master cylinder, rotors, and brakes. Which brings us to the present, I took my car to get my regular service and find out that I have to change my front and rear brakes and rotors. The front I can understand given that it is now at 77,510, but the rear brakes and rotors again after 18,500 miles? I have always felt there is something very wrong with this car and after research on the web and finding others are having similar problems, I know there is something very wrong with this car and when it comes to the brake system there is definitely cause for concern. Though it has only been at inconvenience at this time, I would like it resolved ASAP. With the exception of the brake pads, vw have not charged me for the rotors and though they have said there is not a problem with the rear rotors and brakes and they have been paying for the changes even though it is after my warranty so that leads me to believe that there are many complaints like mine and there has to be a problem.