Carb part wear

Looking at the needle valves, I see a brass seat and a rubber-tipped needle sealing against it. I can see how the rubber deteriorates with age, but since it's softer than the brass it touches, do the seats really wear out?

Also, jets. Jets don't have any other part touching them. Sure, they get gunked up, and overzealous cleaning can ruin them, but other than that, do they wear? How would that happen?

 

But the brass is NOT necessarily "softer" than years' worth of dirt. Quite often you will find a ring worn into the seat from contact with the needle. Usually, the culprit is corrosion though, and the seat becomes pitted.

Jets themselves shouldn't actually wear out.

 

Aha. That makes sense. The needle tips become like a hard pencil eraser, and that stuff is dang abrasive.