Turn signal won't cancel W126
 

At first it was intermittent but now it's all the time. When signaling left, the turn signal will not automatically cancel. I can hear a click as the steering wheel passes the spot where it should cancel but it passes without cancelling. Turning right is no problem. All the lights outside flash appropriately.

I guess there is a piece of plastic in the switch mechanism that has worn or broken off. I've taken the steering wheel off to have a look, but it looks daunting. There are lots of small bits that look like they might be hard to put back together.