Brake Light On problems of the 2002 Lexus LS430

I wanted to write to express my extreme disappointment in my Lexus driving experience. I currently own a 2002 Lexus LS 430 sedan that I purchased on December 28, 2005. Since then, I have had very serious problems with my braking system. First, my vehicle had been in the shop 7 times for my brakes. This is a very serious problem; my emergency brake comes on by itself. While I am driving the brake light comes on, I must pull over and stop the vehicle and pull the brake before the vehicle will move again. My vehicle had been in the shop a total of three weeks for this one problem that is still on going. Everyone in the maintenance department has looked at my vehicle they tell me they can not find out why this is happening. Finally, this vehicle was a pre-owned vehicle that was supposed to have been checked out. Let me tell the real story, first I had to pay out of my pocket to get the brake fixed. The brakes were making a loud noise, I paid for new brake pads that was $75 dollars. Can you explain why I had to pay for new brakes on a pre-owned vehicle? next, the two outside mirrors had to be replaced it was covered by the warranty; again keep in mind I only had this vehicle for five months. My vehicle has been in the shop more than on the road. Lastly, my vehicle is currently in the shop once again for my brake system.