I had the problem with a Gen3 G27. I fixed it with the new .40 ejector.
If you call Glock, speak to the Warranty Service Department and explain the problem, and say you want the new ejector, they'll likely tell you to find a local Glock Certified Armorer to order and install the part for you. You can arrange with them to send it in to them if you want, you might as well ask for a prepaid shipping label but they may not give you one.
If you want to get the new ejector and install it yourself, the new ejector is available in the newest Gen4 trigger housings. So far only MidwayUSA.com and glockparts.com have been confirmed to sell the Gen4 9mm trigger housing w/30274 ejector(both backordered), and only glockparts.com has been confirmed to sell the Gen4 .40 trigger housing w/28926 ejector. The early production "new" ejectors didn't have numbers on them, but here's what they look like:
Because you can't use a Gen4 trigger housing in a Gen3 gun, you'll need to pull the new ejector out of the Gen4 trigger housing and do the same with your Gen3 trigger housing, then put the new ejector into your Gen3 trigger housing to use in your Gen3 gun. If you continue to experience erratic ejection with the new ejector, keep the new ejector in the gun and replace the extractor because the extractor probably doesn't move freely enough.
Remove the trigger housing from the frame, grab the ejector with a pair of pliers and pull it out of the trigger housing, then insert the new ejector. Be careful not to bend the ejector to either side because the slightest change can either adversely affect ejection or put the tip of the ejector closer to the primer of a live round being ejected which would be dangerous.
(I wrap the teeth of the pliers in masking tape so the ejector doesn't get gouged or scratched)