I honestly don't know. I'm not knocking the weight weenie stuff. I have about 6K on my current 105 RD and it works fine. I'd hope to get 25K miles or better, but I guess that remains to be seen. Obviously, those of us who do a lot of hills are going to wear out drivetrain components like cables, STI shifters and derailers more quickly than flatlanders.

My impression is that the lighter stuff in Shimano's lineup isn't any more durable--just lighter.

Anyway, pcad didn't address my technical observations. Just blew me off. Can you believe that? I suspect he's clueless as to why an RD would fail, so I'm sticking with my pivot slop diagnosis. Not that I know, but I do my own maintenance (and I suspect pcad does more than he lets on), and that's my position on the matter. Again, if it's just the spring, you'd think they'd make it replaceable.