Nope. I've had nothing from David Kee. I went to his website and found that the Toploader does have some "yellow metal"--four bronze synchro blocker rings. BITOG (Bob is the Oil Guy) has a short discussion or two, with the claim that GL-5 gear oils, which have more sulfur than GL-4s, can attack the yellow metals, and also that GL-5s are somehow too "slippery" for the Toploader.

I don't consider any of this "authoritative". However, I do know that the gear oil I mentioned earlier, Chevron Delo ESI, has no sulfur at all. Here's a blurb from their Product Salesfax Digest: "They are formulated with ISOSYN base stocks and compounded with a unique extreme pressure additive utilizing an inorganic borate compound. . . . [They] provide a wear protection film three to five times thicker than the conventional sulfur-phosphorus antiwear film. The inorganic borate film is composed of compounds that do not react with metal."

The gear oil is both GL-4 and GL-5 rated and comes in SAE grades 80W-90 and 85W-140. Chevron product is not available in many places, so I don't know if it's a realistic option for you. (Disclosure: I own a few shares of Chevron).