I found that many of these rear derailleur pulley wheels end up cracking, but that doesn't mean they can not continue to provide service. My solution was simple and effective. First wash the pulley wheel in soap and water, then an alcohol bath. When the pulley is completely dry and clean you are ready for two part epoxy putty. The kind I use makes a dark gray final color. Do not try to compress the crack in hope of making it go away. The Campy pulleys crack because of a design flaw and they need this expansion in order to function. You simply pack the crack with the putty and wipe the outside with an alcohol dampened cloth to even out the application. When the epoxy is dry you can then paint the pulley with a little oil paint to cover up the epoxied part. The white wheels will need an off white application and the gray can probably be left alone as the epoxy is a close enough match as is. My experience is that this will prevent further degradation of the wheel and you can continue to use them. No other pulley wheels seem to crack, but then again no other derailleur has the cache of the Campy, so you'll just have to put up with the cracks. It's a small price to pay.
Garth Libre in Miami Fl. USA