Could not really understand the tumbler design until I removed. Have reinstalled now - procedure would be to align the tumblers to position 1 using your key, where you can look from inside the plastic housing up at the tumbler - once you see that small slit, use a very small jewelers screwdriver to push that metal in.

The metal spring action will only be able to push in if the key is inserted and turned slightly right (position 1).

Once you pull inward, the tumbler will fall towards the plastic ignition housing - but you will have to sacrafice 1 of your keys to grind the sides down so the key can pass through the metal collar.

This procedure will save the collar (and ignition housing) from being destroyed by prying it off. Collar's only function it appears is to prevent thieves from easily accessing the tumblers for the car.

Benz really protected the W140 against thieves - takes quite a bit of time to fool around with this well-designed ignition assembly.