Neo's had problems with this too, I hadn't realised that cockers suffered from this. First time it happened we kept thinking it must be his teeth, and kept opening his mouth up to have a look (poor boy).. We were getting to the point where we had to exclude him because he smelt so bad!!!
Luckily the vet picked it up quickly and we used hibiscrub to help clear it up. We generally give both boys a wipe over once a week when I clean their ears.
I must give the apple vinegar a go tho' as that sounds like a good thing!