Automotive Gear Oil GL-4 is a high-quality, multi-purpose gear lubricant specifically engineered for use in manual transmissions, transaxles, and steering gears that require an API GL-4 level of protection. Unlike standard GL-5 oils which can be chemically aggressive toward "yellow metals," this formulation is "synchronizer-safe," meaning it will not corrode or prematurely wear the brass, bronze, or copper components essential for smooth shifting. It is formulated with premium paraffinic base oils and a balanced extreme-pressure (EP) additive package that provides a high-strength film to protect gear teeth under heavy loads. With excellent thermal stability and resistance to oxidation, it prevents the buildup of sludge and varnish, ensuring a clean internal environment. It is the professional choice for vintage and modern manual drivetrains where shifting precision and component longevity are the primary operational goals.