I have an 89 325i that has recently begun having battery issues. Sometimes when I step on the brakes, the radio cuts out for a briefmoment and then comes back on. Today, the battery light remained illuminated until I was a few miles down the road and the radio issue has become far more frequent. Also, I got the 1231 motronic code (low voltage). I know replacing the entire alternator will fix this but what are the chances that it's just the brushes/voltage regulator module?