You need to try a Glock 30274 Ejector. I am assuming the G19 you have came with the 336 Ejector installed in the Trigger Housing. You will probably have to order a new Glock Gen 4 Trigger Housing to be able to get the 30274 Ejector or a Lone Wolf Gen 4 Trigger Housing from Glockparts.com or Lone Wolf. That is the first thing I would try before anything else.
I have a Late 2011 Gen 3 G17 with the same issues. Weak random ejection which sometimes causes stovepipes because the Ejector and Extractor are not working together to really flip the spent case out of the ejection port. I've had 3 stovepipes in the last 600 rounds. Tons of rounds to the forehead, off my lip, grazing the top of my head, and even some go out forward to the right. Know this................you are not the only person in America with this issue. Glock blames it on ammo and limp wristing.
I'm headed to the range tomorrow to see if I can get mine to run with a new 30274 Ejector I just got in the mail from Glockparts.com. Good luck
ETA: For your reading pleasure.
Want Your Ejection Problems Solved? Listen to Dave. - Glock Talk
Glock 19 Extractor Woes
Randy's dissertation on erratic ejection and extraction in the Gen 4 Glock 9mm pistol - M4Carbine.net Forums