You might, if you haven't already, check for tick-borne diseases and do a complete thyroid panel. Both of those can cause musculoskeletal aches/pains that won't show up in any kind of radiology. And either may underlie the bursitis, as far as that goes. If the thyroid is off in either direction, too high or low, cracked pads can result. (At our house the Bag Balm didn't help with that, but his pads normalized when the dog's thyroid medicine was cut in half.) You deserve a lot of credit for all the efforts you've made trying to diagnose and treat him. Hope you can get it completely sorted out soon!