OK Guys, please keep the thread on track without personal attacks.
Wendyj,
As you may have picked up on by now, things that are squeaky clean squeak for a reason. They have higher friction because smooth surfaces tend to contact one another intimately enough for some electron sharing to occur between atoms of the two materials, which acts like little microwelds that you have to keep breaking as you move them along each other. Dillon recommends against SS pin cleaning altogether because their powder measure's combination expander/op-rod/drop tube keeps sticking inside the smooth, clean brass and pulling up hard enough upon withdrawal that when it lets go it jumps suddenly and throws dispensed powder out of the case. Obviously, use of an inside neck lube or brushing the inside fixes that.
Lee's philosophy includes providing functionality at a lower price point than their competition, and one way they minimize cost is by providing no finer surface finish than is needed to make a tool practical. IIRC, in his book, Modern Reloading, Richard Lee even describes how his son found the more economical source of their carbide sizing rings and devised their elliptical inside profile so they worked well with the more economical grade of carbide they get. Lee is ingenious, but if sizing is now producing cases rougher than it used to, something has changed. I expect the idea that surface imperfections in the carbide ring have picked up bits of material is correct. I've also had that happen with more polished grades, though, so they are not a guarantee of immunity.
Carbide rings for straight wall sizing are convenient because you can skip case lubing, but many lube anyway because of how much smoother the operation is when the do.
Gun Scrubber has no copper solvent, per se. It can loosen copper mechanically, but that doesn't generally work nearly as well as actually attacking copper directly. Anything that attacks copper will also attack brass. You can try a copper removing cleaner like Bore Tech Cu++ or KG-12 to see if that clears it. Butche's Bore Shine or Sweet's 7.62 would also work but be slower. Household ammonia applied around the inside of the carbide ring with a cotton swab may work after several applications. (I would use a swab with any of the copper dissolving cleaners; let them sit 5 minutes, then wipe them off.) But if the scratching material is made of nickel, this won't do anything to it. Some guns are nickel plated, so bore solvents aren't made to attack nickel. At least, not on purpose. They won't to attack tiny bits of sand or other grit, either.
You can use an abrasive softer than silicone carbide to remove material sticking out of it. You could try JB Bore Compound or Iosso Bore Cleaner spun on a patch to see if that does enough cleaning. It's the safest abrasive to use. If that doesn't work, you can wrap some extra fine emery paper onto a dowel and polish inside the ring with it. Emery has about half the Vicker's scale hardness of silicone carbide, so it will abrade things less hard than the carbide itself, while leaving the silicone carbide alone. Be sure to flush the die out with your gun scrubber after using any abrasive in it.
If you find you can recondition the die surface like that, I would put some Lee case lube and alcohol in a pump sprayer and treat a batch of cases with it and let it dry before sizing them, then wash it off the cases with water afterward. This should push this dry lube into the carbide surface, so it tends to release things that try to stick there. Other dry lubes may work for that, too, but the Lee lube is not so slick that it affects shooting in a chamber, which is a plus for it. Or you could wash it off with water afterward if you prefer.
Finally, you can always call Lee and ask their advice. They might even offer to fix it for you.