I never looked for it, but Leibniz was a member of the RS so he almost certainly shows up. He's mentioned frequently in the Philosophical Transactions. For example here's "the Answer of Mr. Leibnitz" in response to a letter from "clarissimis viris Newtono" (the most distinguished Newton): https://books.google.com/books?id=7uwyAQAAMAAJ&pg=PA186&dq=%...