1985 123 300D Key will not turn the ignition. It worked nicely for perhaps 15 years, but, now, it will accept the key, but the key does nothing. You cannot turn it. The key is in the off position and can be removed. It sits in my garage (I am thankful it happened here) and I can easily work on it. I have lots of tools, but don't have the foggiest notion as to where to start. I can see a groove between the outer ring of the switch but it appears to do nothing when I insert a strong paper clip. Where do I go from here, other then have the car towed to a dealer, which is miles away..

Thanks in advance.. Ken