FTExtract?

[BPTactical]

The o ring is a supplement to the extractor spring plus it acts as a buffer between the extractor and bolt so you don't hammer the extractor. Numerous sources market "extractor upgrade" kits that include a stiffer spring, revised buffer (the small rubber slug in the spring) and the O ring. Might as well upgrade your entire stable.
Rings are shot, you shouldn't have to hold the BCG "just so" for it to stay extended. Don't worry about the one piece rings or any hoopla, standard rings run just fine.
Both items are a normal wear and maintenance item.
Unless the extractor is chipped, cracked or bent they usually don't require replacement.