Good morning guys.
Here's an interesting discussion of the topic:
https://www.fordbarn.com/forum/showthread.php?t=219484&showall=1#:~:text=GL4%20and%20GL5%20both%20contain,will%20destroy%20the%20yellow%20metal.
Lubrication engineers have told me that the GL5 potential adverse effects on yellow metals can only occur at elevated temperatures (250-300* F) that do not exist in ordinary car and truck applications. So the question becomes whether to believe educated professional lubrication engineers or "anecdotal" opinions.
Ray W
