Thanks, Dana, that helps with what Dennis said last night.  I would assume
that EP additives in GL-4 are sufficient, then, since that's what VW still
calls for.  In that regard, it would make sense to me that the extra
corrosion of brass synchros caused by GL-5 wouldn't be an acceptable
tradeoff for the extra (unnecessary?) EPs in GL-5?

I'd still love to hear any updates/opinions on the subject, since I've just
rebuilt a syncro tranny and have the option to go GL-5 if it makes sense.
Sniff, sniff....her whole life ahead of her....makes a parent proud....  :)

tx,
bmc  :)
"Faith will move mountains, but you'd better bring a shovel...."

>
> Here's a tidbit on the subject:
>
> GL4 vs GL5 from pennzoil's site:
>
> What happens if API GL-5 gear oil is used in an API GL-4 gear oil
> application?
>
> API GL-4 and API GL-5 products typically use the same extreme pressure
> (EP) additive system, with the API GL-5 having about twice the
> concentration of a API GL-4. In service, these additives become active
> under extreme load and temperature when the protective oil film can be
> squeezed away. EP additives work by forming wear-resistant compounds with
> the metal of the gear tooth surface. As the gears mesh, these compounds
> shield the gear teeth from direct metal-to-metal contact that would cause
> wear and damage to the gears. If too little of the active additive is
> present, proper protection would be compromised. Too much of this additive
> could cause excessive chemical corrosion of the gear surface. If an API
> GL-5 gear oil is used in a application where API GL-4 gear oil is called
> for, chemical corrosion of "yellow metal" components may occur, such as
> bronze synchronizers, brass bushings, etc. This may lead to shifting
> difficulties or shortened equipment life.
>
> -Dana-