What happens if you use Mercon LV in a auto trans that takes M5?

Using Mercon LV in an automatic transmission that requires M5 fluid could lead to potential compatibility issues, as the two fluids have different specifications and performance characteristics. Mercon LV is designed for newer transmissions and may not provide the necessary lubrication or protection for older models that require M5. This could result in increased wear, overheating, or even transmission failure over time. It's always best to use the manufacturer-recommended fluid for optimal performance and longevity.