The trouble with antibiotics is that they only work for a certain time (after many doses, they don't work) and they treat rather than solve the underlying problem. Your dog could live to 16/17 (as mine did) and may have this problem for the rest of his life - getting harder to treat. I know you don't like the idea, but I would seriously consider having the surgery now, before he gets older. My Jamie had regular anesthestic up to the age of about 14 because, as well as the cocker mouth problem, he had gum disease and needed his teeth cleaning every 6 months. If the cocker mouth is serious, it would be better being sorted once and for all, now.