It is to help the syncro's bite and aid their longevity when using a synthetic.

Synthetic is a great lubricant. Actually a little too good in this case. But it's extra thermal protection is great for a tranmission.

Also IIRC Ford's new "Honey Colored" fluid for the MTX-75 is basically a synthetic blend with additive itself...

2000 SVT #674 - Check it out!

Whoever coined the phrase; "If it ain't broke; don't fix it" ~ Just doesn't get it...