I rebuild GM power antenna. I have a few for sale but prefer to rebuild your antenna so that we know it fits your fender.
The most common Delco antenna were made from 1980 until the present and I can repair any of those. The standard failure is the motor runs but the mast does not move. This is a broken plastic cord. They are still available but I use a steel cable (wire rope) and it will outlast the plastic parts by a long shot.
Prior to 1980 GM used antenna from Tenna. I can usually repair those but it depends on what is wrong. I do not have a supply of spare parts for the Tenna units, so it is best that we talk before sending me your antenna.
If you have a power antenna that need repair, contact me at (Barney@texas.net) or 512-869-5114
Repair price for the 1980 and up units is $50 plus shipping. Price on the earlier antenna depends on parts availabity.