The great GL 5 debate

Bought some gear oil from screwfix,£ 9.99 for 4.5 litres .EP 80/90 GL 5 .Ive replaced axle oil with it and I was going to replace transfer box oil with it ,but then started reading all sorts of contradicting reports about using it.Some say its got to be GL 4 others says GL 5 is fine in transfer box. Its a 94 auto disco 300.

My diffs are filled with GL4 but the LR spec is the old MIL-L2105 or MIL-L2105B, C, D. Now GL5 although both oils are 80w90EP.

API Category GL-4 designates the type of service characteristic of spiral-bevel and hypoid gears in automotive axles operated under moderate speeds and loads. These oils may be used in selected manual transmission and transaxle applications.

API Category GL-5 designates the type of service characteristic of gears, particularly hypoids in automotive axles under high-speed and/or low-speed, high-torque conditions. Lubricants qualified under U.S. Military specification MIL-L-2105D (formerly MIL-L-2015C), MIL-PRF-2105E and SAE J2360 satisfy the requirements of the API GL-5 service designation.

Now you know.. but some oil companys in their spec sheets for the disco recommend GL4 (Castrol) or GL5 (Comma) I couldn't be bothered looking at the rest of the oil co's specs.

Regards

There was a fred about this about a year ago.
The concern is that GL5 attacks phosphor bronze bushes.
The concensus was that it's OK in Defender and Disco Axles, but not in the Transfer Box - that needs GL4.
GL5 is a no-no in Series Axles and T/F Boxes.