Does Chapter 18 advocate for keeping a Guru's teachings secret? What justification does it provide?

No, Chapter 18 directly refutes the idea that a Guru's teachings should be kept secret. The author calls this belief a "meaningless fuss" and "merely imaginary." The chapter argues that not only direct instructions but even spiritual insights received in dreams should be shared with everyone for their enlightenment. As proof, the text cites the example of the sage Budhakaushika, who narrated his dream-vision of the Ram Raksha initiation to all. The chapter reinforces this by comparing the Guru to monsoon rain clouds that shower the water of self-bliss on everyone with love, without restriction.