On the additive , I read the TSB on Alldatapro at the P. Library. I can't remember for sure but I think it being for all V5MT1-1 thru 1-3.
I ran all GM synchro for 5 years. Then GL5 w "equatorc"(sp) for a year, yikes!
Very recently : 2 quarts RedLine syn. 79-80,,,1/2 quart Pennzoil synchromesh,,,1 pint stalube 80-90 GL4.
My trans is the first really bad one, truck built in 88. It has white paint on the fill plug , which means it went in on the semi recall and had that kit they used for mine . They have another kit for the 90-90.

It seem real thin,,,when I grind the gears there sharp clash noise. It shift better when I've had a dose of cafine. Still slow on 1 to 2nd, I usually shift slow , and click it to 3rd without releasing clutch ,,then to 2nd. Works real smooth that way.