[Fot] GL-4 question

[jim hearn]

I might have missed this but what is desirable about GL-4 versus GL-5, etc.
for use in a Triumph (TR6) tranny?  I see non-synthetic StaLube is GL-4 and
so is a version of Redline gear oil.  It doesn't seem like they could be
equal if judging by nothing else but price.  Does it just say that both are
adequate for this application but GL-5 is not no matter what brand?  Thanks
for any clarification, Jim

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