The extractor likely has one of the problems listed above.
The first thing I would check is for the build-up of gunk behind the extractor limiting its movement. Some solvent and compressed air, or spray gun cleaner (wear eye protection) can clean the build-up out.
After a thorough cleaning in the extractor area, and being very safety conscious, I would hand feed and extract a mag of cartridges to check for proper function. Matter of fact, a "before and after" check with the hand feeding and extracting might be a better idea. Do it in a safe place/direction. Don't touch the trigger.
The extractor spring and claw would be next on my list to check. I believe the Glock forum may have "how to replace" info available.
Last edited by 1SOW; December 12, 2011 at 01:57 AM.