If it's dual rated GL-4 GL-5 on the bottle you'll be fine.
The additive package for GL-5 use to attack the yellow metal (brass, bronze) in the synchros. They've either changed the additive package or added more additives so that doesn't happen anymore.
The only possible problem would be the GL-5 is too slick for the sychros. If that happens, take it out and save it for the transfer and diffs.....
