You might want to go over to the 107 forum, here: R/C107 SL/SLC Class - Benzworld.org - Mercedes-Benz Discussion Forum
A bunch of seriously dedicated nutcases on a very active forum.
Before you start this job, get replacement bulbs for any burned out ones you have in the cluster.
First, disconnect the battery and turn the ignition switch to position 1, this unlocks the wheel.
To change the lock cylinder, you'll have to pull the instrument cluster, which means pulling the steering wheel. To pull the steering wheel, you need to pull the center part off,to expose the large nut that holds the wheel on. Put a piece of board from one of the wheel spokes to the floor, when you loosen the big nut in the center, you want to work aganst the wood brace. DO NOT try to work against the steering wheel lock, it will probably break the wheel immobiliser.
When the nut is removed, you should be able to pull the wheel straight towards you. This will let you get to the cluster. The official tools to pull the cluster are a pair of hooks with handles, but you can make your own out of a coat hangar. About 10 inches long, with a 1/4" hook at the end. You slide them into the gab between the instrument cluster and the dash, and turn the hooks inward and pull when you can't go in any further.
The cluster should pull out to where you can get your fingers behind it to pull off the electrical connectors, unscrew the speedometer cable, and loosen the oil pressure guage line.
DO NOT EVER try to start the car with the cluster removed. The oil pressure guage is hooked to an oil line that is connected to a fitting on the engine. If you start the engine, you will have that line pointed at your torso, spewing (possibly hot) oil right at you. You will wnat to see how much oil your clothing can absorb before you can get it shut down, otherwise the oil will be on your upholstery.
When you have gently disconnected all the connectors from the back of the cluster, you can lay it aside on a soft cloth to protect it. You can now change out any bad bulbs, repaint your needles, or fix your clock, if necessary.
The lock mechanism is in three parts; The cylinder/core, the wheel immobiliser, and the switch. There is a black heavy plastic cover over the cylinder area that may need some 'persuasion' to slide toward the back of the car, aout of the lock hole in the dash. There is a flange/ring in the plastic cover that fits into a groove on the immobiliser mechanism, since the plastic is old and stiff, you need to be careful, yet firm.
When the plastic cover is removed, a spring loaded part will be exposed, that needs to be pushed inwards. This will let you pull the lock core out by the key. Reassembly is in reverse order.
Here is a thread from the 107 forum that has a video and pictures.