The text states that only Brahmins like Radhakrishnabai were allowed to perform important services for Sai Baba. Is this correct?

This is a misunderstanding of the information presented in Chapter 35. The text actually highlights the opposite. While it mentions that Radhakrishnabai was a Brahmin "worthy of worship by all," it specifically praises her for undertaking what was considered a menial service: sweeping Baba's paths. It states, "this dullness of thought never touched her faultless heart." The chapter also makes it clear that this same service was performed by Balaji Patil Nevasakar before her and by a devotee named Abdul after some time. This shows that service to Baba was not restricted by caste or social standing, and that devotees from various backgrounds performed acts of devotion.