Newer vintage Gen3's have been having ejection problems as well as the Gen4's. Here's a
post I made on an earlier thread. As an update to that thread, after my ejector change I have put over 2000 rounds through that gun with no malfunctions at all.
Just because an ejector change fixed my gun doesn't mean it will fix yours. But if cleaning and lubricating it doesn't make the problem go away completely, something's probably out of spec. Whether you want to DIY or send it back to Glock is your call.