I bought a few pairs of pulleys earlier this year, and when I went to use them tonight, 3 out of 6 of them were cracked and unusable.
I think I'm going to stick with all metal pulleys from now on.
EDIT: The ebay vendor I bought them from immediately offered to replace them. It never hurts to ask! Thanks to vendor "3dfactory" - anyone can get bad product, the good vendors take care of their customers when it happens.