Novak suggests using GL-4 gear oil, because the lower sulfur content is easier on the synchros. They know more about these than I do, so I'll trust them on this one. I figure it will be fine with whatever GL-4 oil my FLAPS has on the shelf. But, if I do run across some Red Line MTL (which is also GL-4 spec) I won't turn it down, as that stuff has been very good to the stock transmission in my 220hp turbo Miata.
