40153-ZVT-A10 Case (Lower) Seal B - Overview. The 40153-ZVT-A10 Case (Lower) Seal B is a crucial component in Honda marine engine systems. This part serves as a lower case seal for the lower unit of Honda outboard motors, helping to prevent water intrusion and ensuring the lubricant stays securely within the lower case assembly. By maintaining the integrity of the lower unit, it supports the smooth and reliable operation of your marine engine and protects it from potential damage caused by leaks