How do you know that a gearbox is not working properly?

Signs that a gearbox is not functioning properly include unusual noises such as grinding or whining, difficulty shifting gears, or vibrations during operation. Additionally, if you notice oil leaks around the gearbox or overheating, these can indicate internal issues. A decrease in performance, such as reduced power transmission or slipping gears, can also signal a malfunction. Regular maintenance checks can help identify problems early.