Welcome to YT and I'm so sorry about Lucky.
Sadly, most vets know so little about liver disease in Yorkies that they don't do bile acids testing soon enough. Most dogs with this disease are diagnosed at a much longer age (before a year or two). Is it a liver shunt or microvascular dysplasia?
The L/D he is on, is it canned or dry?
Is he on Denosyl or Vetri-DMG?
Is he on lactulose and vitamin e?