Before you order one, pull the cylinder out of the assembly and check it. Yes the cylinder does fail. But the ignition assemtbly also fails. My wifes car, where the assembly connects to the switch broke. The replacement I got from the junkyard the mechanism that actually disengages the steering wheel lock was worn out and didn't work properly. I would check all this stuff out ahead of time. Since I bet the dealer will be hesitant to take back a cylinder that matches your car.

And removing the whole thing is actually quite easy, once you know what you are doing. I've removed these things so much in the past 2 weeks I can yank one in about 4 minutes. I've taken tons of pictures and I'm in the middle of making a DIY page for boostnbenz's site.

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'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.