I did this repair back when I owned a 123. The center vent actuator is always the first to go - it's out front right under the dash where it gets more heat from the sun than any of the others. I'd characterize the repair as more tedious than difficult. There's no rocket science involved - just follow the instructions in the manual to disassemble everything. I didn't completely remove the dash from the car - just getting it to where it could be pulled out of place several inches was enough. Think it took about 4 easy hours - I work pretty darn slow.

- Jim