I never thought about the mouth problem as he does not having a problem eating when he does eat, biscuits or dry. As for his weight I can ony guess but im virtually 100% sure he is not loosing weight. As for your comment about getting nicer food, I cant see how, as I have every type of food going and some is very expensive high quality stuff.
One thing I will say is that it might be to do with the fact he has no collar on. After you lot scared me to death I took it off, so maybe one of the old dears thinks he is a stray. I might have to get a collar with do not feed written on it.
One thing he will eat is donner meat, he is mental!! (dont have a go he doesnt get much, its just he growls when he eats it so I do it occasionally only)
He has been sort of fussy for several months. I dont mind the changing of minds in regards to what he likes and doesnt but he sometimes only eats a small amount of his fav food where as in the past he may have eaten it all.