I wonder if that AD is the TR health check. Where you check the TR brake actuator and Center drive unit. The Flex lines on this check as you apply the brake and lock it on the tr brake actuator, keeps the flex line from turning, and you turn it a certain torque with a torque wrench. To see if the brake is doing its job by holding the flex line. Sometimes they break and you have to order a new flex line. Other times the brake don't hold and you have to change the tr brake actuator. It's an easy check when you know what youre doing and you have a good inspector with you.