And to add, because some of these tubes and NOS antenna complete assemblies and repair parts have the PLASTIC cable per original, they age in the box/package and you still run the possibility of them not lasting all that long. There seems to be a fix though with an aftermarket STEEL cable replacement. It's simply the top section of the antenna and you'll need to swap that out on a tube or complete unit if you don't want to have problems with flexing 200 year old plastic and hoping it won't break in 4 or 5 years, or months, and you'll be doing this again. In your case because someone broke yours off, you got to get a good working mast assembly first. It seems it has the incorrect finial on top for the Cutlass (not sure about other makes) but if you have yours, you can swap it out or simply leave as is.
If you just need a repair kit for the cable and top section of the mast (includes bottom seal, cable, top mast- but not the finial) and absolutely WANT a GM part, it's GM part number 22038195 superseded to 19151297. I think the only reason they even do aftermarket replacement cables now is because the same part fit Corvettes. Those guys always get repro stuff made. But if it fits our cars, it's a win!
Again, not cheap, but it's around the going price of the repair cables that are plastic, maybe just a couple bucks more but shipping is included for $51.99 from Mike's Montes. He's not the only one out there with them, but it's just one option. And should last a whole lot longer. I'm considering doing this on my 87 442 since the cable finally gave up the ghost and I'm going to have to swap it out with a new tube assembly. I have the assembly, just haven't bothered to do it yet.
http://www.mikesmontes.com/78-88-G-Body-Steel-Power-Antenna-Repair-Kit-Free-Shipping_p_2837.html