Fluid change - recommendations

[Dicky]

Dave, I can give you my thoughts on gear lube.
Make sure its GL4 only, not GL4-Gl5.

Seems everything other than GL4 has Chlorine in it,
and eats yellow metal (copper, brass etc.) synchronizers and such.
some possible brass washers in rear ends. This of course applies
mostly to cars of this vintage.
GM P/N 89021671 Additive P/N 88900330 Most Chev. dealers will get it.

I use a Brad Penn GL4 lube in tranny & rear end with the GM additive in RE.