John,

I dont have a w123 so I cant help you with the release button. But I did have to replace middle mechanical section (not the tumbler nor the switch)(ignition lock? maybe)on my W124 I dont remember there being an issue with finding the release button though. It was accessible without removing column nor cluster. Ok so the whole reason for my post was I thought the switch was bad but it wasnt. It was the T-shaped post (aluminum)from the mechanical section to the switch had broken allowing the accessories to be powered up but not engage starter when turned to start position. Original switch was fine and still in service. Either way ignition assembly has to come out to get to the screws for switch. Sorry about the lack of info on your current removal hitch but just wanted to pass on my experience.

Arlo

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W211 E550
HVAC/R Certified Technician