40103-ZVT-300 Case (Lower) Seal - Overview. The 40103-ZVT-300 Case (Lower) Seal is a critical component for Honda marine engine systems. It functions within the lower unit sealing system, playing a vital role in creating a watertight barrier around the lower case assembly. By preventing water intrusion and maintaining lubricant integrity inside the gearcase, it helps to ensure seamless integration with existing parts, maintaining optimal performance and durability.. Key Features. Precisely engin