On high-mileage Berettas, the locking block can shear off one of its lugs, rendering the gun inoperable. Not really a safety issue, though, at least as far as causing shrapnel damage to the shooter or anything like that.
Its actually pretty rare with the M51, but was all too common on the early M92s. The M92 locking blocks underwent at least 3 revisions to mitigate the problem and replacement parts are common for those, but unfortunately dont fit the 51.
Now, the Egyptian Helwan copies of the M51 used softer materials (or had improper heat treating) resulting in more block failures.
I would inspect (and grease) the block once in awhile, say every 500 rounds or so, but wouldnt worry about it too much on a training/range pistol. Still, a spare would be nice to have if it could be found.
Improved for the M51? Ive never heard of such a thing.....do you have a link?