OTS/CSO select

My son is active duty Air Force and was picked up for OTS. He was selected to be a CSO. He joined to be CCT and wound up a year later getting reclassed for two much magnesium in his urine. That’s since fixed itself. He did however have a kidney stone, very mild and hasn’t had any since. While getting his flight physical the doctor told him he’d need a waiver. He’s completed four years now with no further issues. The doctor said he didn’t know if this was waiverable. Any expertise on this out there would be appreciated.