Took Ruby in today for a moist 'sore' like spot on her lower lip that's been there a few weeks. My hypothesis was right: her teeth are pretty flat and her lower lips 'plump?' - (I think the vet said) and she must be constantly leaking some saliva in the same spot. It's sort of oozy damp gross about 1/4 inch wide by maybe an inch and a half long. Vet called it Chelitis and gave me a bottle of chlorhexidine to treat it with daily at first and then use as maintenance cleaner a few times a week once it settles down.
This will probably be something we have to deal with from now on and I was curious if people had experience with it in the long term.... sorry no pix but it's sort of hard to see anyway. I haven't consulted the google yet on this but intend to soon.