The serial number tag is located to the SWIVEL BRACKET (port or starboard); or, check the INSTRUCTION PLATE, Positioned amongst the thumb screws above the steering tube. Thankfully, PartsVu provides a prosperity of resources to help you find the Mercury outboard parts you need to keep the engine running efficiently, https://emilianojhari.madmouseblog.com/17476057/yamaha-250-outboard-top-seal-for-lower-unit-an-overview