Does Chapter 18 support the idea that a Guru's teachings should be kept secret?

No, Chapter 18 directly refutes the idea that a Guru's teachings should be kept secret. The chapter addresses the notion that what a Guru tells one person should not be told to others, calling this "merely imaginary and a meaningless fuss." To support this, it provides a powerful example, stating that the sage Budhakaushika narrated the dream-vision of the Ram Raksha initiation to everyone for their enlightenment. As Chapter 18 further illustrates, the Guru is like the rain clouds of the monsoon, showering the water of self-bliss with love upon all, not just a select few.