BEIJING, Oct 20 (Reuters) - China's market regulator said on Friday that Tesla Inc will fix software for 4,787 imported Model X cars due to an issue with the brake fluid sensor. The action is described as a product recall under Chinese regulations, the regulator said, but it was not immediately clear if drivers might need, or would be eligible, to return vehicles to Tesla for refunds. (Reporting by Brenda Goh and Qiaoyi Li; Editing by Alison Williams)