GL4 and GL5 Vs Bronze Bushings

All GL5 gear oils use Sulphur as the agent that protects the gears. That's why they all smell so lovely.

These components are inherently aggressive to anything with copper in it (brass & bronze included).

If you can get away with a GL-4, use that instead as it has less active chemistry. This is OK for lightly loaded gears working in the same plane, but definitely not for hypoid axles.

People try to mitigate the effect of this chemistry as best as possible, or compensate for it, so there are better and worse products. Nothing will be “safe”, it's just degrees of good-enough to bad.

GL-5 allows for a corrosion rating of a “3” in a particular copper test. Some others specify better than this, e.g. MAN 342 M2 or M3 or S1, which require a “2” in the same test. One of our more common products gets a 1b.

To buy some MAN lube (don’t google it!), a list of approved oils is below.

I recommend something with both MAN 342 M2 and ZF12E approval: https://www.zf.com/global/media/en_zf/lubricantslists/TE-ML_12.pdf

There is also a product from our competitors that gets good performance, but it tends to be pricey stuff. Look for MB235.8 approvals for that.

Given all of that, Castrol EPX 80W90 could be a good choice. Likewise Shell Spirax S3 AX.