Well, on closer examination of my extractor depressor plunger (henceforth called EDP) I discovered that JBS was right after all. What I thought was a ring is actually wear (scoring). The slide is digging into the front end of the EDP. And this is after only 500 rounds! No wonder people are experiencing trouble a few thousand in: parts are wearing out. I swear, Glock has really gone downhill.
Anyway, I took the plunge (no pun intended) and made myself an EDP out of a nail. Filed it, stoned it, honed it, and smoothed it on my wood lathe. Then polished it on the buffing wheel. Then hardened the Hell out of it with Kasenit. Then had to buff it out again. File won't touch it. Probably won't wear out. I only hardened the contact surfaces at the front and back.
I used JBS's idea of lengthening the wider portion at the front, and at the back as well. Also, I did not make a point at the back of the part the spring slips onto, but left it blunt. It is butting up against the blunt end of my spring loaded bearing (SLB), so I saw not reason to sharpen the end. I did make sure that the overall length is within a thousandth of the original part.
Took it out and shot a box through it. Didn't make any difference as far as ejection goes. Probably last longer though.
I fault Glock for not taking the sharp edge off the front of the hole these parts fit into. There's no reason the EDP should be getting beaten up like this.
The picture shows the original part and my homemade job. You can see the scoring starting on the front of the Glock part. Time will tell if mine does any better, but I can make one in an hour if I need to. I'm also going to add a touch of grease at the front from now on. Might help. I'll keep it out of the extractor itself of course.