The thing is that even if he is Clear for fanconi there are many other diseases that we don't have DNA tests for and the only way to reduce the risk of producing them is to know the health status of the dogs in the pedigree. Do you have any way of verifying the health of your dog's parents? How about his siblings? If not, you could very well be breeding a dog that is at high risk for producing PRA, a late onset disease that causes blindness, or hip dysplasia which can be produced by dogs that are phenotypically normal but have affected relatives, or hypothyroidism.
This is why people are urging you to neuter your boy. You have no way of knowing what he carries genetically and since he was from a pet store there is no reliable way to get depth of pedigree info on him.