The wire does deteriorate. While you have the replacement out for the smoke, take a look at the others and see what else has cracked or brittle coating or solder that looks like it’s about to let loose. Anytime you can head an issue off at the pass, you’re ahead.
I have purchased a used ZW. The fellow who did it did a great job on the innards, but I'm wondering now how I clean the fairly small tracks that the rollers are leaving? Or do I even worry about it? I'm getting great performance and voltage.
Many thanks in advance
The rollers are essentially made of pencil lead. They may leave minimal trace marks. As long as they are making good contact and rolling freely, it isn't worth worrying about. Totally different story if the rollers were not properly installed and do not roll across the copper windings. If they drag across essentially stationary, then they need to be redone properly.