The book states that Das Ganu advised Ratanji to seek help from Gajanan Maharaj. What was the specific advice given?

This question contains an incorrect premise. The source material from Chapter 14 explicitly states that Das Ganu advised Ratanji to visit Sai Baba in Shirdi, not Gajanan Maharaj. When Ratanji confided in Das Ganu about his deep sorrow over not having a son, Ganu's advice was, "Go to Shirdi; you will obtain your heart's desire." He further instructed Ratanji to "Take Baba's darshan, bow at His feet, and tell Him your secret from beginning to end." There is no reference to Gajanan Maharaj in this context.