40204-ZV0-700 Extension Case Grom - Overview. The 40204-ZV0-700 Extension Case Grom is a crucial OEM rubber seal designed specifically for Honda marine engine systems. It supports the gear case extension by ensuring a secure, watertight seal that protects the internal assembly from water intrusion and debris. This part helps maintain reliable operation and longevity of the marine engine by preventing leaks and contamination. Engineered to integrate seamlessly with existing factory components, it