I am so sorry to hear about the weak rear legs. My grey, Brandi, five years ago got weak rear legs but she had only been off the track for about 6 months. Took her to holistic vet right away and he did the acupuncture/chiro and she has been on supplements ever since. They don't know why her legs were weak. Think something neurological went wrong. I think the acupuncture will keep your grey walking. Also prednisone has helped. We wish you the best.