Success. I went and bought a #54 drill bit which fit perfectly and by turning the lock bezel slightly as I pushed the drill bit outwardly I was able to unscrew the lock bezel and remove the tumbler. Thanks everyone for your help.

I am still wondering how a 3 year old MBZ tumbler failed so quickly. I only use a single key (single key on my key ring) and only drive the car under 5000 miles per year. The entire switch mechanism is 3 years old also. Go figure.