AMC Gearbox Oil

With the advances in oil tech , my opinion is that there are probably better choices availiable now. I suspect that many use the same oil in engine and box. SAE 50 is a bit heavy for our climate so many use SAE40.  I have used HD 30 , SAE 40, 20/50, EP 80 , EP 90 , and ATF for a time ! . No problems at all. I think that sleeve gear bushes benefit from a thinner oil than SAE 50.  or EP90  which are  a bit too static in my view. More important is the need to drain and refill  annually to remove water which can enter through cable hole or vapour pressure. I expect this thread will run and run as everyone has an opinion on oil.

My absolute favorite is 75W-90 full synthetic, Mobile 1 or Valvoline SYNpower. Extreme high/low temperature protection.

Brutally cold shift from neutral to 1st is so much easier that is VERY evident. No desire to go back to other types.

No idea if it is available in UK/EU?

I also have one bottle of Best Parts/Autozone 75W-90 labeled and packaged as STP brand  no mention of synthetic or maker. Never tried it...

From memory I think that 75/90 ep is thinner than sae 50 at the sort of temps we have in the uk  , so should get round the box and into close fitting bronze bushes ok , I have also heard that  fully synth oils tend to stay put and give better start up protection , so agree with Dave , I like fully synth for the engine too , but a 20/50  would be my choice for the sort of use we have for classics in the  UK . 

Yes gear oil viscosity is very different  . I don’t think the problem with corrosion to bronze bushes exists anymore