Basically it sounds to me like cooper has a tendon issue on his kneecap(patellar subluxation if I remember right),I had that same injury on my field trial dog years ago,because it is a tendon it takes along long time for it to heal due to mimimal blood flow in tendons.It took a year for my dog to heal up from it and in that year he wasn't allowed to run,he was kenneled in a 6x12 the entire time.My vet diagnosed it with his hands,unsedated by manipulating the dogs knee through it's range of motion and feeling the tendon.It's a good thing you've got a stand in with the new wirehair.