It's number 5 in the pic below. You'll find it underneath number 8 when you pull it from the wheel. It will either be stuck to the wheel/bearing face or to the underside of number 8.
I have 76K miles on mine. I'm not sure of the tolerance - I just remove it, clean and inspect it to make sure it's not cracked, and give it another shmear at every final drive service (+/- 10K miles).
