I have the same problem. It's not in the knowledgebase. Help identifying the part would really be great because it's not user serviceable and sure looks like it's a design flaw.
Did find this though: http://www.tomtech.de/spareparts/tt/ger/PDFDokumente/Xerox/Drucker/Laser/sw/Phaser%C2%AE%204600_4620...
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Recently, my Xerox Phaser 4600 had a gray rubber belt break off. I have located where it has come from but am not sure what it is called or if I need to replace just that rubber piece or other parts associated with it. Please see the picture below. I wanted to upload a picture with more detail but the site has a very small upload limit. Thank you in advance for the help.