I don’t know of any symptoms, but I replaced the one in the front of my propshaft because it looked visibly damaged (see image in first post). However, after removing it and looking at it, I think that as a bush it would still have functioned perfectly fine. It’s just that the very front rubber lip with a spring inside, which I expect is a moisture or grease seal, was visibly damaged. But the tough nylon(?) tube inside and then the rubber material that bonds it to the outer metal tube was as good and solid as anything.