I had a similar symptom - could not shift the lever left into S mode, but the problem turned out to be more prosaic...
Opened it up with help from the video from post #48, but wish I had looked at it first before trying the gearknob, as it came off suddenly to hit me in the left eye, just as the video warns!
My wires were fine (2010 335i) but the plastic ring that holds the shifter boot had broken and lodged into the shifter parts. Don't think I can buy a replacement but the boot seems to hold up fine without it.
I did free the wires from that awkward fold though, so hopefully won't get any broken wires in the future!
