4 speed oil change

OK,
Put 50/50 in it. That's 50% Old style ATF(like Dextron III), and 50% EP anything under 100. No additives of any kind. Roadtest it. If it grinds, put new brass in it and deglaze the cones. The longer you keep grinding it, the more it will cost to repair.Pluck it it out early and it will be just the brass and gaskets/seals.I've been running this 50/50 since 1971.I tried other stuff and other ratios. 50/50 works.
You put that thick stuff in there and maybe it won't grind; but it will also be the slowest shifting tranny ever! Unless you have it behind a slanty; then I guess it won't make any difference, cuz you have to wait for the revs to come back down anyways.......lol