GT6 Tranny and Diff fluids

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I'm planning on installing the rebuilt diff this weekend on the GT6 (note
crossed fingers and toes).  What fluid should I be using, GL-4 or GL-5, or
doesn't it matter.  I also want to change out the tranny oil, which should I be
using.  I don't remember what I used last, I think it was GL-5.  What about the
Redline stuff?

Mike G