Slides and locking blocks appear to be the only parts that have any history breaking.
The slide issue was corrected in the early production of the M9. It was found that some of the early M9 slides would fail when fired with higher than spec ammo because there was a problem with the metal in some of them. The tale has taken a life of it's own, and if you ask people, you'll find a bunch who will tell you they've seen broken slides, etc. when in reality they've never touched a Beretta in their life. There WERE slide failures to be sure. Most were traced to some of the SEALs using MP-5 ammo which was specifically loaded to higher pressure. The Army did find some bad slides as well, and ordered a one time replacement at 1000rds for the ones already in service. Those slides were returned, inspected and modified to standard, or junked. Since the early days, and the one time slide swap out (there was no way to tell if a slide was really bad, so the Army did what it always does. It swapped them all out at once so they knew they were all good) there have been no slide fractures.
Locking blocks fail once in a while. They are supposed to be swapped after so many rounds. Supposedly they are supposed to fail before the frame. There are some vendors who offer an improved part, but as the block seems to act as a "fuse" I'd do some research before buying one. It might be the way to go, or it might not, I dunno.
The SB's are VERY high quality built guns. The fit and finnish is wonderful and quite frankly better than today's production. They just seemed to be a better quality, but maybe it's just preception. Anyway, I wouldn't worry about it any. The only slide falilures seem to be limited to a couple of early contract US military guns.
Ross