Maybe this will help ?
I found it from another forum
Soap residue, sweat, dust, dirt gets in the space around the outer button, so that it no longer acts as a spring loaded, self-returning button. You will see this if you remove the movement from the watch case and look at the little metal plungers under the four outer buttons and the “start/stop” button. Use some silicon lube or spray on the outer portion of each button and around the small metal plunger inside while you work the button and the plunger back and forth, until it no longer hangs up and glides freely. Clean/dry excess silicon. Check the corresponding areas on the sides of the watch movements (what the little metal plungers hit) to make sure the metal spring prongs are straight and not corroded (use emery cloth or steel wool to clean if they are).