After reading this post and the referenced posts, I decided that I should be proactive rather than reactive on the switch of my 1995 E320 wagon. Several months ago I had the key not want to turn but with a little jiggling it turned. I removed the key and sprayed some lubricant into the cylinder and everything has been working fine since then. Reading this post made me realize that I should have a closer look before it was too late.

I made a tool from a piece of coat hanger, went to the car and turned the switch to the correct position to insert the tool. Inserted the tool and couldn't get the cylinder to release. After several attempts it finally released and I removed it. I then turned the key and removed it so that I could take the black bezel off. A couple of small pieces had broken off and fell out as I was removing the key. This could have failed on me at any time!!!

I will use a screwdriver to start the car for a couple of days until I get the new cylinder.

Thank you everyone that made me nervous enough to check mine out!
This only takes a few minutes and is well worth the effort. Sure beats having to struggle with it when the key locks up and won't turn.