Deca may make joints feel good, but actually, just mask damage or pain. Winny may actually repair joints but make them hurt. Your tendinopathy is a combination of tendinitis that is aggravated by tension and movement and tendinosis that is healed by tension, that is why it never goes away. You can do it if you get the right combination of tension and strengthening without aggravating. Injuries that are counterintuitive in some way are the hardest to cure. Most are. With the muscular issues, it's usually the "opposing area" from the where the issue is and "neurological not muscular." Retrain the neurological patterns of contraction for the opposing muscle/area, problem fixed.
Healthy tendons are made up of type I and repaired by type III, I don't know if supplemental type II would be effective, whatever the case, repaired tendons are more delicate at least temporarily.
All awesome info, although I would say that low T may reduce collagen synthesis, when I had my biceps tendon re-attached, my surgeon told me that TRT would speed healing, he was one of the team doctors for the raiders and sharks too, did a great job on my biceps.