Hey Guys,
I bought my '73 GX Coupe (A15, Original 4-speed Gearbox, Original Diff) about a year ago with a lot of vibration and whining down the driveline. The first thing I was advized to do was squeeze about half a cup of copper compound grease into the diff with ATF and the 85W gear oil. The gearbox just got ATF. Its been a year and the vibration has quieted down quite a bit.

I'm thinking of replacing the diff and gearbox oil this afternoon and I was wondering if anyone had advice or hints on the type of oil I should use. Maybe some mixes that work better? In example, a friend of mine mixes a third of his diff oil with another type of oil into his GTX's diff. I just can't remember what it was. =/

I live in South Africa, I do just as much highway driving as I do bumper-to-bumper driving, and the the drivetrain's (original) been hammered by an A15 for 10 years.

Any advice or hints would be appreciated.