Do not take the key out!!!! Get the tmbler out to inspect first. You must have the key in to get the tumbler out and if it is broken, you may never get it back in!!!! Removing tumbler with key in is about 10 minutes. Dealer quoted me 10 hours labor if the key cannot get in!!!! there is 'space metal' in there.

Here is procedure I copied from my service manual -- take a look at the other posts on the subject. This is for a W124, don't know particular differences about an S class:

If you can get the tumbler to position “1” the procedure to remove is simple, with a Key intact. If you are stuck in “1” DON”T MOVE IT!!! May be tough with a broken key in there (little or nothing to pull on) but can be done. I recently had my tumbler break. Those suckers are tough to drill out in order to keep the crooks out! Drilling is an ordeal. After about half an hour of finessing, I got mine to "1" and removed it quite easily with directions from the service Manual using "Self Made Tool" as follows (and I quote, with annotations.) It came out in 4 pieces. I got a new tumbler, including a key, to match my VIN and the other locks in the car for about $75 from Caliber Motors in CA. Order your new stuff now, whether you are drilling or removing, you'll need it. It takes about three days.

1) Remove cover (black plastic one around key area, lift carefully from Steering column side)
2) Turn Key to “1”
3) Introduce releasing wire [Note:] through bores (two little holes in the silver part of the assembly) in the locking cylinder. Then push down on releasing wire and unlock the locking detents by overcoming the resilient resistance. (Push on that wire, hard, you may or may not feel a ‘pop’ and then pull in the cylinder at the same time!)
4) Remove Locking Cylinder including covering cap from steering lock by means of ignition key (or a hook you might have to make to get a purchase on the thing. Since you don’t have a full key in there, you may be able to get the cap off first, and then get a tool, like a needle nose vice grip, on the tumbler.)
5) Remove releasing wire from locking cylinder. Turn ignition key to “0” and pull off.
6) Remove cylinder from Covering (black) cap. (Keep this cap, order a new one if it is damaged)
Note: the releasing wire of 2 mm steel wire is self made according to the specified dimensions. Straight length of wire = 300 mm. (Make two bends 20 mm apart to form a ‘U’. Grind the tips to a 70 degree angle, inside angle (the tips of the angle grinds are on the outside of the ‘U’)(Stiff, but not too fat coat hanger wire might just work. If not, get some good stiff wire.)(Start car carefully with a screwdriver while the thing is off. DO NOT break anyting in there as you will have more to fix)

Installation (Here I am not direct quoting)
1) Insert Cylinder, make sure the elevated ridge lines up with the housing (about 10 o’clock)(it’s a good idea to lube all the parts on the car and cylinder while you have it open.)
2)Place black covering cap on and line up the little notch to the left (about 9:30)
3) Turn locking cylinder to “1”, then force cap and cylinder into steering lock while making sure that both parts are engaging. (Might have to wiggle the whole thing a bit while you push)(The key should point to the “1” notch on the black cap to indicate you are in alignment)
4) Make sure it all works
5) Install plastic cover

__________________
David
1986 300E Anthracite + ECodes + MB Mileage Award