Other than the well known spring issue with the Gen4 Glocks, there is also a lesser known issue with the ejector, which has now been redesigned by Glock. Your best bet is to call Glock and have them replace the ejector with the new curved ejector.
Recent discussion on GlockTalk Forum:
Best way to sweet talk Glock CS - Glock Talk
Video of the ejector old issue:
http://www.youtube.com/watch?v=8Qd-MT98WZU&feature=mfu_in_order&list=UL
Video of the new new ejector:
http://www.youtube.com/watch?v=6bnptOAR_SI&feature=mfu_in_order&list=UL
Recent discussion on GlockTalk Forum:
Best way to sweet talk Glock CS - Glock Talk
Video of the ejector old issue:
http://www.youtube.com/watch?v=8Qd-MT98WZU&feature=mfu_in_order&list=UL
Video of the new new ejector:
http://www.youtube.com/watch?v=6bnptOAR_SI&feature=mfu_in_order&list=UL