I don't know much about liver shunts, but thought they were in puppies only? Something about a vein not sealing itself off so the liver can't do it's job in cleaning the blood. If that's the case, he would have been showing symptoms much much younger. Again, I don't know much about shunts, but just my initial thoughts.
Seizures are so scary. Scrappy started getting seizures and he ended up passing the same day they started. They were only about 30 secs long each. I would suggest get every test done that the specialist recommends, and if they can't find anything, please get him on meds that will keep the seizures under control. If he does have another seizure you have to hold him until it's over so he won't fall over and hurt himself. I'm so sorry you are going through this. It's such a helpless feeling and you want to help them but don't know how you can.