Ringworm is contagious and can be given to other animals and humans.
I just read through everything. I wouldn't do the sulfer dips because it stinks and i think it dries them out more. If you suspect food allergies, the duck and potato is a good food but you must ONLY feed this food and nothing else. No treats, no table scraps. Just this dry kibble. It can take up to 3 months to see results but stick with it. Also you can add fish oil and vitamin e to the food. I use this one
http://www.healthypets.com/deei8oz2ml.html
also, make sure you brush him every day. this will loosen up the dead skin and make him less flakey.