I suspect the contacts on the TouchShift are dirty. I had this problem on my W163 and I took it apart to clean them and did a write-up on the job. The disassembly of the console on the W209 is not exactly the same, but once you get into the TouchShift itself, it similar enough. See if this might help (if you are so inclined for the DIY job):
http://mercedesml.info/touchshift/index.htm
http://mercedesml.info/touchshift/index.htm