I lost one early, around 30,000 miles I think. It had a couple of stone holes, broke right thru the middle of one of those holes.
I replaced another at about 80,000 because I had the inner primary off for another problem and it was looking worn.
My dealer told two years ago I should replace one on another bike because it had about 30,000 miles on it. I was headed on a long trip to some pretty desolate territory so considered it, but passed. It has another 25,000 on it now.