Odd how this subject popped up, as I've been researching this as well for a couple of days. The GL-4 is what many recommend, but I see many, many using GL-5 and not reporting problems after running for years. However, I do prefer to err on the side of caution, but GL-4 does not appear to be as readily available. Additionally, I've found that Sprawl-mart 80W90 has the following printed on it "The heavy duty extreme pressure formulation protects against rust, foam, high temperature, and corrosion of copper or bronze bushings".
I've read that some recent formulations of GL-5 have addressed the yellow metals problem, but Sprawl-mart is the only GL-5 label I've found that alludes to yellow metal compatibility. Regardless, it still states to be used where GL-5 is recommended (legally covering their ass). Also, would like to know who manufactures and bottles Sprawl-mart oils (still don't know); NAPA oil is Valvoline.
