On a variety of Lexus vehicles, the power antenna mast can be removed from its motor housing by first, removing the antenna head retaining nut that hold the top of assembly to the vehicle body, turning on the radio and pulling out the entire mast along with its plastic chain cord as the antenna is rising.

Likewise, a replacement power antenna mast can be inserted into the motor housing assembly by feeding the plastic chain cord into the assembly with the teeth on the plastic cord  facing the same direction they were facing when removed, turning off the radio and letting the motor drive the plastic cord into the assembly.

Note: there is no need for wheel well access to the motor housing as this replacement  can be accomplished from the outside of the vehicle. However, there are several problems that you should be aware of and hence, the main reason for this guide.

First, when feeding the plastic chain cord into the motor housing, it will most likely run into a shelf at approximately one foot down inside of the housing. To get past this shelf, you will need to uncurl and make as straight as possible no less than one foot of  cord and blindly try to fish the cord past this shelf.  You can tell when the cord has reached the winding gear by the feel of a slight resistance as the cord  moves into the gear teeth rather than the abrupt stop felt when the cord hits the shelf.

Secondly, make sure the new mast when fully extended along with the plastic cord are both exactly the same length as the original. For example, if the new mast fully extended is longer than the old mast but both cords are the same length, or the new cord is shorter than the old, then after the retaining nut is replaced, what could possibly happen is that the motor electronics could drive the cord completely out and past the gear teeth causing the antenna to not fully retract when the radio is turned off. Hence, you will need to turn the radio off and on several times each time its used to get the antenna to fully extract. A backup timing circuit on the motor housing pc board is suppose to keep the antenna from over traveling, however, it easily  gets out of calibration.  If the plastic cord is too long, then you will hear a grinding noise as the motor tries to wrap excessive cord around the internal plastic spool near the end of the down position, and thus, the antenna mast may not fully collapse into the body.