Hyundai Tucson 2013 has an automatic transmission problem

2013 Tucson automatic, clean engine, transmission has slack in third gear, needs changing. The car drives normally except for the slack in third gear only. New Nexen tires, used for a week. The car is standard automatic, electric windows, air conditioning works cold. The car is priced at 15,000 from the transmission shop owner. Chassis is required. The body has been sprayed for cosmetic reasons. Needs vehicle registration renewal 400 SAR 0537760005 And inspection