Darn, this is the THIRD time I write this!
I don't think it would be liver. Liver disease does cause seizures but it's only on the very last stages that this happens and there are myriad other symptoms that appear before the seizures: overgrown beak and nails, greasy and/or bad plumage, fatty cysts and/or xanthomas, accumulation of ascites, discolored urates and poop, disorientation and lack of balance, etc.
I would definitely ask for a bile acids, mind you, because I am sure that there is already damage there (and I would put him on a detox regimen asap - I do this to every older birds or any that has been in a bad diet for a while) but I would also ask for hard metal testing and an ionized calcium test because both low calcium and metal poisoning are causes of seizures. Lack of vitamin D3 and A can cause seizures as well, but you are already taking care of that. The other two possibilities are chronic dehydration (much more common than people realize, especially when they don't eat fresh food daily) and what they call 'stress seizures' or 'racing heart syndrome' but I am not sure if I believe this actually exists because it sounds like one of those 'catch-all' default diagnosis that vets give you when they don't know what the heck is going on (the other one is allergies). Low or high sugar in the blood can also cause seizures but the vet would have seen this on the blood work recently done.





