Ask you vet about Adequan injections. It's not pain killer, but a compound that goes through the synovial fluid and lubricates the joint (HEALING), with strong anti-inflammatory effects in about half of dogs. It prevents further cartilage degeneration. There are many threads about it here -- it's a 4 week loading dose, 2 shots a week, but I've seen radical improvements in some seniors (one of my oldsters went from slow ambling on walks to trotting like a youngster in 3 weeks).
You'd probably be better off just feeding food (animal parts, not kibble) loaded with bio-available forms of glucosamine/chondroitin (like dried beef trachea), instead of buying it as a supplement. (See bestbullysticks.com for a source of trachea tubes, if you need one -- dogs LOVE chewing on them.)
The evidence that regular chondroitin supplements help arthritis is not strong. A 2010 meta-analysis of 10 trials concluded there was no benefit. The supplement industry's claims got way, way ahead of the evidence:
There is ONE high-quality study that a patented, low-molecular weight form of glucosamine and chondroitin owned by NutraMax labs has good results--but that's the only supplement form that seems to have any proven benefit in dogs (NuMax makes Cosequin and Dasuquin). I like the Dasuquin Advanced supplements (RX only, from vets) because they include MSM, curcumin extracts, boswellia, avocado soybean unsaponifiables (ASU), and some other compounds that seem to help. It's kind of pricey though, and you might be able to buy some of those "good" ingredients separately for less -- the "Advanced" version isn't available online (vet clinics only):
Landmark Clinical Study Confirms Effectiveness of Glucosamine Hydrochloride and Chondroitin Sulfate Combination in Supporting Joint Health
I don't have an experience with green lipped mussels, but I've read that study results have been mixed. Try it and see -- it's supposed to be very safe. This link says two of the five trials in humans found a benefit -- not great, but suggestive that maybe some dogs will benefit and some won't:
Natural Eggshell Membrane supplements are worth trying. There's one promising study showing it helps arthritis, and I've seen good results in my dogs too. It's very safe, not terribly expensive, and thus worth considering:
Type II Collagen/Hyaluronic Acid might also help. It comes as a supplement, or make your own in some chicken/turkey bone broth made from necks and backs. I think Gatorbytes and Carmspack have some posts in the archives explaining how.
This is also helpful:
As for the liver, before you start throwing herbs at it, I'd like to know WHY the numbers are off. It's a sign that something's going on...what?