I'm glad your gun is working and you like it. I also have a new US Glock that is at about 375 rounds that's been good to go. But the multiple replacement guns I've had one was good for 800 rounds before problems. Another was good for 2000. Three weren't right out of the box (two GEN3's, one GEN4). I am convinced that the two that went for several hundred or a couple of thousand rounds the MIM extractors were soft.
And no I'm not saying MIM parts are all bad. In fact for years before I retired we made engine parts with an MIM type process. If held to tight quality requirements and done properly they are usually fine. I wonder now sinc my new gun is back to a non-dipped design if their is a flaw in the dipped extractor design. Mines been fine also but I have the APEX set up just in case. But I don't think it's just one problem that's causing the issues.
As I and others have tried different after market parts amd fixes to get the guns to run right. Some fun after you change this part or that part. Some it dosn't matter what you do. Or what Glock does for that matter. My last GEN4 problems showed up right away. They simply said they couldn't fix it. Some of the guns they tried simply completely rebuilding the gun. Worked awhile.
Kind of surprised your gun is a GEN4 and still has the 336 ejector. For quite awhile now the GEN4's have come with the 30274's. The GEN3's usually the 336. But as others have said if it's shooting fine right now I don't know if I'd mess with it. As I said earlier changing different parts has got some guns to work and others not. For right now I would just shoot the snot out of it as others have said. If it goes sour call Glock.