Correct! Basically, I excluded the bad range so Linux doesn't touch it. It's been stable for weeks now. I should send the DIMM back under warranty.

Don't send it back. Since they can't easily replace it with new hardware, they will probably refund you the price of purchase. Which is normally a very good deal, but obviously not in these circumstances. I've seen it happen with GPUs as well.

I'm convinced it's not worth the hassle!