
Think if he is developing deep cracks you should at least check with the vet, even if you are correct and he is short of some needed elements, you need to know what, any why. It could be the diet but just as likely that part of his system is not, for some reason, dealing with the food he gets in a proper manner.
Treating with bathing and some sort of softening cream (I used Zinc and caster oil) will not hurt but you need to know why he has the problem.