In some cases this might be true. Certain types of EP additives are designed to react at elevated temperatures to protect metal surfaces under extreme lubrication conditions. Such additives are often called “chemically active” and at high temperatures (higher than 140 to 150 F), they can indeed begin to react with yellow metals. This is why it is so important to be careful when choosing gear oils for worm gears in order for the gears to function properly. A good way to check if an oil is “chemically active” is to look at the specification sheet provided by the oil manufacturer. On the sheet you will typically see a test called “copper strip corrosion” (ASTM D130). It tests how chemically reactive an oil is to copper or copper-containing alloys. For gear oils, a rating of 1a is typically a good indication that the oil is chemically inert; higher ratings (such as 1b or 2a) can indicate possible problems when used in certain gears at high operating temperatures. Often, a lubricant manufacturer will specifically state that “this oil should not be used in gearboxes containing yellow metals”; other times they will state that the oil is only suitable for application on steel, meaning that they should not be used where the ring gear is brass or bronze.