I just replaced my defrost vent actuator on my 86 560sl. It can be a ***** to get to, I had to remove the console to get to it. The acuator is on the left upper side of the radio. it is a dual acuator that can be removed and repaired or replaced. it has three wiz nuts holding it on the bracket, I broke the actuator removing it. I bought the acuator for my 86 about a year ago and had read that you have remove the dash to service it. to install a new one you have to remove the wiz nuts to get it out or take it apart to replace the diaphram.

86 560sl
94 Chev S10