One of the problems with retract servos is the end point is not adjustable making adjusting the linkages critical.
Too slack & the retracts won't move & lock, too tight & you fry the servo.
Spektrum have released a retract servo that you CAN adjust the end points.
http://www.spektrumrc.com/Products/D...odId=SPMSA7000
Could be the answer? - John.