How do you know when to replace a gearbox?

You should consider replacing a gearbox when you notice unusual noises, such as grinding or whining, which can indicate internal damage. Additionally, if you experience inconsistent performance, such as slipping gears or difficulty shifting, it's a sign that the gearbox may be failing. Signs of oil leaks or contamination can also indicate the need for replacement. Regular inspections and maintenance can help identify these issues early.