Can you use gl5 gear oil instead of gl4 oil?

Using GL-5 gear oil in place of GL-4 oil is generally not recommended, as GL-5 contains additives that can be harmful to the yellow metals often found in older gear systems, such as brass or bronze. While GL-5 may provide better extreme pressure protection, it is designed for different applications than GL-4. If your vehicle specifies GL-4, it's best to stick with that to avoid potential damage. Always consult your owner's manual or a professional mechanic for specific recommendations.