Stickiness on the leaves of most plants is simply the sign of aphid or other sucking insect damage, as it's caused by the sugary sap excreted by them in feeding.
If you mean there is something visibly sticking there, it could be some sort of scale insect. As sarcococca is an ornamental box, you could try a systemic insecticide or just leave it, for natural predators to get under control (the best method).