Reply to OldNuc:
GL-5 does not play well with the yellow metals.
The oil companies currently claim that new and improved additive compounds, to GL-5 (EP) gear oils, means that they are now compatible with all metals.
There is is debate amongst chemical engineers about how bad the problem used to be anyway, with a polarity of opinions from "hogwash" to "big problem".
In essence, GL-5 (EP) gear oils used to contain an EP additive called organic sulfur compounds. These compounds are somewhat unstable, and have the unique ability to "flash weld" themselves to steel surfaces under extreme load. Under high contact pressure, the surface of the steel (gear tooth) reaches localised high temperatures (300-1000°C) and the sulfur compound welds itself chemically to the gear surface, creating a highly stable and very strong, and smooth surface, that resists gear spalling and metal-to-metal contact.
The sulfur compounds formerly used, would attack and etch copper, brass and bronze components that were regularly used in older cars, trucks and equipment.
The problem did not occurr until the sulfur compunds reached elevated temperatures, around 120°C (250°F).
Thus, many engineers decided the problem was "hogwash", as they claimed that that temperature was rarely reached. In operation, 250°F oil temperature in gear compartments IS reached on a regular basis .. thus the problem was real.
The oil industry is constantly changing its additives, because they keep finding new additives with improved properties over previous ones. Sulfur compounds have been eliminated from EP oils and have been replaced with newer and better organic compounds, that perform better than sulfur compounds. Organic sulfur compounds were being eliminated from EP oils in the 1950's, and there are none used in EP oils today.
In addition, copper, brass and bronze components have been greatly reduced in manufacturing useage in recent decades .. not only because of the cost .. but also because high grade steels have been able to replace them.
If in doubt, ask your oil supplier if their EP, GL-5 oils are compatible with copper, brass and bronze metals. You will find that in almost 100% of answers, the answer is Yes.