Opinions on Synthetic Transmission Oils?

[Glenn Kaufman <gkaufman@ftp.com>]

Does anyone have any opinions and objective data on synthetic transmission
oils?  This weekend I'd like to change the oil in my transaxle in my 86
Coupe GT.  Last summer, I added Penzoil's dino transmission oil.  Since the
weather has been getting colder, the trans takes awhile to warm up.

I've been happy using Vavoline's semi-synthetic motor oil and am considering
putting in their full synthetic tranmission oil (GL4).

One interesting note, last time I was at Valvoline, I was told that GL5 is
just the newer version of GL4.  I believe that one of our members pointed
out that the difference is in the amount of zinc?  or another metal within
the oil.  Can someone remind me of the difference?

Thx.  glenn