Drained the old lube out of my four speed to replace 59 year old gaskets. The lube is a sludgey in the bottom, suggestions for what to flush it out with.
Marvel mystery oil comes to mind,

Thanks for your input

I always like to drain fluids when components are hot but I know that is not always possible (especially on classic cars). If you have it apart and are going to reseal it how about remove the side cover and dump it on its side and let it drain drain drain (like overnight). Same thing on the differential (remove the top cover and dump it upside down).

Thanks Timothy, doing the trans now, it’ll be like that for a couple days because I have other things lined up.

Diesel fuel will cut the sludge, so will gasoline.

1964 Monza Coupe
1965 Corsa 140
1967 Monza Coupe

Maryville, TN
U.S. 129 The"Tail Of The Dragon"

If the transaxle is out of the car (which it sounds like it is), you could turn it upside-down or on its side (as mentioned above) and blow solvent into it to flush out the old lube. Something like this would do the trick:

[www.amazon.com]

James
65 Corsa
SF Bay Area