To determine the year of a Kubota KX251 based on the serial number, you would typically need to refer to the manufacturer's serial number charts or contact Kubota directly, as these charts can vary by model and year. The serial number you provided, x30425x, suggests that it falls within a specific production range. However, without access to the specific serial number database, I cannot provide the exact year. It's best to consult a Kubota dealer or their official resources for accurate information.