I am so frustrated!!!

I have spent over two hours trying to remove the ignition switch/lock on my 1979 300 D. I know that the repair manual, and other comments in this forum say that you should be able to insert a small screwdriver, or paper clip, in a slot or hole to hold the locking pin in place while you turn the lock for removal. Problem is, I can't find a hole or slot on the lock...and I've looked hard...not on the face of the tumbler where the key fits in, or on the body of the lock. The only hole I have found is on the side of the backend of the lock, near where the vacuum cut-off switch is mounted.

HELP!!!!

 

Also...I'm not sure which lock tumber set or ignition switch is for this car...all of the web sites that sell Mercedes parts list several switches depending on the VIN. The trouble is, my VIN (as found on the window column, the driver's door post and the title) is not like anything described anywhere. The VIN for this car is a sixteen digit number (no letters) that starts with 123130. Can anyone shed any light on this?