I've searched and found that GL-4 gear oil should be used in my transmission and everyone seems to be using redline oil for their transmissions. But I can't find any gear oil that is only GL-4. My question is can I use Valvoline 80w-90 gear oil even though on the back of the bottle it says, "Recommended for all hypoid differentials (conventional and limited slip) and manual transmissions where an API GL-4, GL-5 or MT-1 fluid is specified."