Alfred sent me a message off forum asking if I had any insights and or photos of how the early ignition lock and switch works.
First of all it sounds to me like the using of a different key to make the starter engage is just buying some time. I don't think that you have realy fixed anything. I would think it is more likely the electrical switch in the photos Alfred has posted.
When I went to start up my car after it had been sitting for 25 years, I had the same symptoms, The key would turn on the ignition and the fuel pump, but the starter motor would only engage by turning the key with excessive force.
I found out that there is nothing in the key tumblers or locking bolt that will prevent the key from turning from the run to start position, The stop is inside the electrical switch assembly, with the switch removed from the lock the key will turn past the point where the starter would engage. The switch containes a mechanical lock out that prevents the starter from engaging a second time unliss the ignition is turned to the off position. It is usuall a failure of this lock out that prevents the switch from engaging the starter.
The tell tale sign that the key tumbler is about to fail is a crack becomes visible below the key, on the side of the tumbler where the flat side of the key goes into the slot.
The single sided key is a completly different lock assembly than the one used in the later 250 and the 280's. The 230 and 280 locks are not interchangeable the /8 steering coulmn has a different configuration for the collapsable steering hub.
The tumbler for the double sided key can be removed and replaced, but the lock assemby with a single sided key was designed as a sealed assembly. The chrome bezel is atached to the housing by two steel pins that are driven into the housing, and are almost impossible to remove.
I took pieces from a 230sl lock, a 67- 108 sedan lock and one of several electrical switches i had and made one complete woking unit out of it, Sorry i didn't take pics, and I'm sure I pitched out the pieces i didn't use so i can't make photos now. sorry.
Just as an experiment, I took one of the /8 style plug in style switches just to see if it would fit the early lock housing and work. And yes it does, I then soldered the plug into the harness, and now have a working radio accessory position on the key switch.