I just recently purchased a 1988 Audi 80. The owner had changed the battery right before I bought it, and the anti-theft stereo system needs an unlock code now to work. I called an Audi dealer and they said it would be $76 for them to take it out and find the number. Is there any other way I can get the unlock code? The owner says it's written down in the owners manual, but it's not.