In my 20+ years of suffering through EC. I am coming down to similar conclusions, of it being caused / related to dry mouth. The causes of dry mouth are several, like you and others have posted, so to find a universal cure might not be possible. Perhaps this is why EC heals for some and not for others even though they used the exact methods that cured one person.
On a side note, I have also tried numerous diet and I feel the same as you, paleo seems to be the most helpful.