Mo. Rev. Stat. § 379.201: Motor vehicle policies to include coverage of owner and vehicle loaned for demonstration or during repairs.

Every motor vehicle liability insurance policy insuring a motor vehicle licensed in this state must extend its liability coverage to include any other motor vehicle operated by the insured individual if the other motor vehicle is loaned, with or without consideration, to the insured individual for demonstration purposes or as a replacement vehicle while the insured's vehicle is out of use because of breakdown, repair, or servicing and if the other motor vehicle is loaned by a person, firm, or corporation engaged in the business of selling, repairing, or servicing motor vehicles. Such extension of liability coverage must include coverage for damage to the loaned vehicle.