Just thought I'd share what happened on my 2009 E90 M3. Build date is July 2009.
About a month ago, I noticed the bank of turn-signal LEDs on my left taillights flickered whenever I unlocked the doors. Upon closer inspection, 3 out of the ~15 LED's appeared to be really dim compared to the rest. Then I started getting the "left rear turn signal malfunction" message intermittently whenever I used the blinkers.
Anyway, long story short, I brought the car to the dealer and they replaced both Left and Right outer taillights under warranty.
Below is the TSB (SIB-63-06-10) for this issue. According to the TSB, the cause of failure is internal corrosion.