40204-ZV5-000 Extension Case Grom - Overview. The 40204-ZV5-000 Extension Case Grom is a vital component within the Honda marine engine systems, specifically supporting the extension case system. This OEM grommet plays a key role in sealing and safeguarding the extension case housing, preventing water ingress and cushioning against vibrations. Engineered to meet Honda's strict factory specifications, it ensures seamless integration with existing parts, maintaining optimal performance and durabil