I'm so glad you responded again. I couldn't find your question in my files of questions that were waiting - somehow it was miscategorized. I looked and looked last night. I do apologize.
It sounds like you are very educated in all of the areas you are dealing with - that helps alot.
I would be suspicious that even though most of the new NSAIDs are a bit different, they are still similar and he might have the same effects. Previcox is one of the newest that are supposed to not affect the GI tract as much, but on occasion it does, too.
Synovi G3 was very popular at the clinic I worked at for and it was very palatable. I have never read the flavored ingredients to see what it was - but it looked as if it would be beef. The clients and patients liked it. One that I would recommend for Calvin with his other problems would be just a straight out capsule of glucosamine and I believe the name may be Dasiquin, but I'm not 100% sure. You could be human glucosamine and chondroitin as well. One thing that we found to be very effect was Science Diet J/D and Purina's prescription food (the name escapes me right now) for joints. I don't know about the beef/chicken in them, though.
I had never used adequan as a doctor because initiially it was cost prohibitive. The cost has come down SIGNIFICANTLY over the years and I had a case that came to me a few years ago that we were out of options. She was an 18 year old cocker spanien and VERY arthritic. We tried everything and she could not tolerate the side effects even with GI protectants, etc. Similar to what Calvin's case sounds like, other than he is so young. So we sent her to a specialist and they put her on adequan. I purchased it for her and we started out with injections every other day, then every third day, then every week, then every two weeks and I think the best we could get her to was one injection every 3 weeks. Some patients can get one shot per month. It was incredible how much it helped her and how wonderful she felt on it - no side effects at all. That made me a believe in adequan and I used it on any case that showed side effect to NSAIDs from then on and have never had a complaint. For Calvin's size the shots would be pretty cheap, probably $10 per shot.
I think adequan would be the next method to try for Calvin. The other thing that would be great for him is to get in contact with a veterinary physical therapist. They can evaluate him and come up with a home program you can do to help him and have good ideas reagarding the neutriceuticals and herbal therapeutics.
Hope this helps,