Brake Light problems of the 2004 BMW Z4

I had this car built and I am the only owner and driver. I have had a personal mechanic take meticulous care of it over the years and the car is stored for approximately 6 months/year because I do not drive it in the snow, and frankly, hardly drive it even when raining. However, it never fails that each year some warning light goes on for no apparent reason. Last fall it was the abs light and the brake light. My mechanic put the car on the computer, and found no issues. Now again, this spring it started out as not being on, but within 5- 25 minutes (varies each time when I start the car up and drive) those two lights come on. Every year there seems to be new lights that come on for no apparent reason. I haven't driven the car more than a few times before a light comes on. It's cost me so much in diagnostic time. Also another problem is that often the radio doesn't turn on. When this happens, the screen also does not pop up. I have to stop the car, turn it off and then restart. Most times the electrical system seems to �restart� itself so that the radio turns on and the screen pops up. The electrical system in this car has never been right.