Although Valvoline, which does not have a GL-4 synthetic gear oil, had some claim their sulfur additives were 'stabilized' or some such thing, and therefore ok.
At one time, Mobil claimed something similar for their Mobil 1 75w90 gear oil.
However, Toyota has specced the Aisin (Toyota subsidiary) R150F trans for GL-5 gear oil. After draining the factory fill at 4000 miles, it ran great on the Mobil 1 75w90 GL-5 gear oil, for the next 13 years.
I only switched to the Redline, because I knew from racing experience that they were great performing oils, and I could get it for a better price than the Mobil 1.
TheDurk said:It seems pretty clear there is a problem with GL-5 in synchronized transmissions with yellow metals.
I definitely wouldn't use a GL-5 in a trans that wasn't specced to use it. Not all manual transmissions are built with the same materials in them.