Headset plastic ring broken: glue or replace?
 

My new-to-me bike has a Shimano STX headset with a plastic ring that's cracked. It looks to me that its function is as a dust and moisture seal. Am I right about that?

Should I attempt to repair it with some epoxy or the like, replace it with an rubber o-ring (presuming I can find something suitable), or would I be better off asking my LBS for a replacement?

Grainy photo:
http://bikeforums.net/attachment.php...hmentid=401160

I've used a rubber band cut from a discarded tube in a case like that. But if you can find a replacement, that's neater.