Just thought of another answer to your inquiry:
have you thought of gluten and casein connection?
Casein is the main protein in milk product, not digested well
by most individuals, and gluten can be responsible for the leaky gut Syndrom even without any laboratory signs of gluten sensitivity. Both casein and gluten have been connected to arthritis. http://www.greenmedinfo.com/blog/gluten-punishment-whole-grain-assault-health?