I'm going to replace the gear oil in the transmission/transfer case on my dad's '63 CJ5. No one knows when it was changed since it was originally my grandfather's. To give you an idea, the differential oil was black. It doesn't see much use and only drives around the farm. I noticed driving it that it's impossible to downshift. It clicked when researching that the brass synchronizer is likely worn out, possibly from a non yellow metal safe gear oil being used. I have no idea how the fluid looks. I ordered VP classic 80w90 GL4 for the transmission change and Mobil 80w90 GL5 for the differentials. Would Blackstone be able to tell me if the previous oil was yellow metal safe?
