Turns out he did not have a sore on his mouth. His mouth looks a bit odd because of lack of teeth. He does have a lot of tartar on one of his few remaining teeth, though vet did not think it was causing him pain. She doesn't want to subject him to a GA for teeth cleaning at his age unless she is clear that there will be a benefit to him. She thought his condition is quite good, but he had lost weight since last July and he is very small to start with, and doesn't have spare weight to lose. He is being reviewed in four weeks because of the weight loss.
Last night and today he only nibbled even at the pate type food, which is worrying me. He did, however, wolf enthusiastically some torn up ham I used to tempt him. Not sure whether to be worried or whether my chai is being jerked, as otherwise he is active and of good form.