I have shod and barefoot horses and ponies with the help of two very good farriers. I think a very good farrier who is willing to explain his methods should be your first port of call. Get one who knows about barefoot methods or search the net for a local.
Secondly I agree with a suggestion above by not oiling everyday to maybe once or twice a week and soaking the feet with water for at least 10minutes a day. The hoof wall needs moisture to remain pliable and the oil may be stopping or robbing this.
Ask your farrier about bevelling or the mustang roll as you may know it, its like rounding off the foremost edge of the hoof (normally left flush when shod). This will improve function and guard against splaying or cracking. You may need to give up some normal routes if you choose barefoot until you have established a well formed and hardened hoof but it may be worth it. :)