Headrest motor adjustment

The headrest in my 94' e320 wasn't working so, after searching the archives, I got the seatback off and found the offending part. The white plastic gear assembly broke apart. After examining the part, it appears that the motor overpowered the gear assembly causing it to separate and crack. The question is, is there a clutch type adjustment on the headrest motor to stop the gears from turning when the headrest is at either limit so that this will not happen again?

Bump

Just in case anyone would like to know, I think I figured it out.
I took the seat back off the other working headrest and looked at it. It appears that the motor just stops turning due to force. My advice to all is when adjusting the headrest, back it off from max up or down by a hair, this releases a great deal of tension on both the plastic gear mechanism and the cable that connects to the motor. Could save headaches down the road.