I took him to the Vet School and Dr. Mansmann and Farrier Kurt vom Orde worked on him for me. Andew, Dr. Mansmann's Tech did a great job keeping a hold of him when Chester kept wanting to leave. Dr. Mansmann said he feels like that is extra thick hoof wall hides the white line until it is really bad and that all the prior damage to his feet (from before I owned him) makes him more likely to get it again!
So in the stall he goes. Hoof drying treatments, including bleach and some baby diapers are in full swing. Guess all my expectations of trail riding him some this summer are on hold again!
Thanks Dr. Mansmann & Kurt vom Orde for all your help!