I've broken the bolt stop block off the extractor ring on a 308 action, though that was on an across-the-course rifle that had at least 9-10k rounds through it at that time. It locked up the action, but I cleared it, shot an alibi string and carried on for the day.
I've also had a bolt sleeve lock disappear. Easily replaced with wisner parts and peened the retaining pin so it didn't happen again.
