I don't know if your car is similar to mine, but I've got an '85 300D and when my turn signals stopped working it was because the hazard light switch was in the 'on' position. As soon as i turned it off they worked again. Of course, the hazard lights don't work. Evidently the hazard switch beneath the button stops working easily and when the button is on, it prevents the turn signals from working.

I understand the switches are widely available in junk yards and easy to replace (at least on my car). I will try this soon. Good luck with your car!