Broken Plastic Ring on Fuel Injector

[Jag1980]

Just took out the fuel injectors on my mothers car -
1998 Buick Regal Supercharged.
I noticed when I pulled them out, the plastic ring is broken on one of them.
I tried searching online for a replacement ring and I see nothing at all anywhere. So I think I'm not going to be able to get them anywhere..
My mother needs her car, so I was thinking.. Can I just put on a new rubber O'ring to give it a good tight seal and install it back on the car broken? I think since most of the ring is still there that the distance will be the same and the new O'ring will keep it from leaking?
I don't think I have many options..

Also, is it necessary to change all the O'rings on all the injectors?
They are not hard like plastic, there still have a rubber feel to them.
If I do change the rings on them all, I think I have a good chance of breaking more of these plastic rings as they seem to not come off very easily.

Does anyone know that exact name for this broken part?