Well, elevated ALT can mean several things. It can be a fluke so to speak or a temporary thing if perhaps the dog is recovering from an illness and the liver has been insulted by said illness. Or it can be indicative of liver disease. But I would demand that your vet be more specific with what he is treating. He says that Bandit needs to be on SamE for life, ask him why? What is his concern,etc... Is he concerned that Bandit has liver disease, if so, what type? What about having a bile acids test done? I really would just go over everything with your vet. He may have a diagnosis and treatment plan in his mind but he needs to share it with you!
Also here is a pretty good link to understanding/reading lab results-http://home.gci.net/~divs/disease/lab_tests.html