Can you elaborate on the leela where a devotee was cured of an ailment after feeding a black dog on Sai's advice?

While you're asking about a leela involving feeding a black dog, the provided source material from Chapter 41 does not mention this event at all. The narrative in these passages is centered on Balasaheb Deo and his spiritual quest. He was a devotee who, despite his strong intentions, could not manage to read the Dnyaneshwari with any regularity. Chapter 41 explains that even when he took a three-month leave, he found himself reading other books but was unable to fulfill his desire to study the Dnyaneshwari, eventually deciding to wait for a direct command from Sai.