Thanks for that information and for the link. That is an interesting site. I am inclined to agree what I have is probably a replacement for stripped out threads.
I contacted the eBay seller for the listing I found, Carb Junky's, and asked this:
Hi, can you tell me some details about this part? I just pulled the needle and seat from my Quadrajet carburetor number 7028219 and it looks very similar to this one you are selling, with the double o-rings. Do you think I may have the carburetor's original style seat, as in this is they way they were made? Or is this style seat a modification done at some point later in the life of the carburetor, such as drilling out threads and using this style seat as a fix for stripped threads? I am finding little information about this style seat online, so wonder if you know more about it. Can you tell me if it is known to be the correct fit for carburetor number 7028219, or can you tell me what the size of the metal part that has the o-rings so I can compare it to mine? Thanks, David
They wrote back: It is a repair needle and seat. There is only one style, so if yours looks the same this will replace it.
So, I'm thinking about ordering that, and see if it fits.