It is possible that part of the toothed plastic of the antenna mast that engages with and coils around the gear inside the power antenna motor broke off in there, preventing the new mast from retracting fully. If you get behind the passenger side fender liner you will see the motor wrapped in plastic attached to a bracket with one 10mm bolt. It is possible (although annoying) to pull the motor out far enough without disconnecting any electrical connections to be able to remove the plastic wrapped around the motor and the screws that hold the gear mechanism in place. Once removed from the motor housing the gear splits into two pieces and you should be able to clean out any broken plastic remaining in there and hit it with some fresh grease. Reattach the motor to the bracket, and then with the car radio on feed the new antenna mast back into the motor by pushing the toothed plastic down through the antenna hole in the hood and into the tube of the antenna motor with the plastic teeth facing toward the opposite side of the hood. Have someone turn the radio off, and after a couple seconds the motor will engage, pulling the new antenna mast down, then replace the black plastic ring and chrome locknut thing and you should be good to go.
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