Pre stretching cable/ Prop differences
I don't think cables stretch. Has the Golden gate bridge started to
sag? I would look for slack coming from your servo moving as the
rubber gommets settle into the mounting screws or nylon horns
flexing or horns compressing into wood or crimpeded clamps slipping on cable or as happened to me allthread horn on rudder
bending. Study the hole system carefully and I think you will solve
your problem.