I don’t have a degree in engineering but even I have the common sense to understand that a static piece of plastic held against a high revolution metal chain at 40 ft lbs is a recipe for disaster. There seems to be plenty of room in there so why didn’t they install some sort of roller tensioner (like some foreign bikes use on their drive chain) or better yet why hasn’t the aftermarket come up with one? And if there’s just no way to come up with something better, at least make them easy to change!
Anyhow looked at mine yesterday and here’s a pic of the front, back looks about the same…they have 27k miles on them. I know they are pitting but I decided to wait a little longer before I change them, just don’t have the time to undertake such an involved project right now.