GL-5 fluid OK in OD tranny for GT6 and TR6?

[Steve Myers <mountainunicycle@yahoo.com>]

Anyone know if using GL-5 rated gear oil is OK for OD transmissions and 
differentials on GT6s and TR6s?

I heard recently that GL-5 must *not* be used because it damages the 
guts (copper seals?). I got some GL-5 full synthetic since I couldn't 
imagine what harm this could do, but figured I'd check with you folks 
before I poured it in.

Thanks!
Steve
72 GT6
71 TR6