A person who is engaged in the business of leasing or renting motor vehicles to others and who, in connection with such business sells any used motor vehicle to a purchaser for his use and not for the purpose of resale, is a retailer engaged in the business of selling tangible personal property at retail under this Act to the extent of the value of the vehicle sold. For the purpose of this Section, “motor vehicle” has the meaning prescribed in § 1-157 of the Illinois Vehicle Code, as now or hereafter amended. (Nothing provided herein shall affect liability incurred under this Act because of the use of such motor vehicles as a lessor.)