Here is part of the post that Doug provided on locking block repair:
I do know, that in the past 25 years, I've reworked more than a hundred locking bolts, And the only time I've EVER seen a top lever problem (as when a top lever has broken), was when the locking bolt was worn to the point that the gun wanted to open while it was fired. Many times when the top lever approaches that 6:00 position, or even further to the left, this begins to happen. A new top lever replacement is not cheap. Preventitive mainenence is. Jack (MIA) mentions I file the locking bolt for a perfect fit. I don't file. On the older Perazzis, I recut the lug on the bbl's to a slightly lesser angle (8 degrees). This gives me a nice square, guarenteed flat surface to work with. When I weld the locking bolt, I do not use an extremely hard welding rod. I like to see as close to possible of equal hardness of the bolt and the bbl lugs, with the bolt just slightly harder. When refitting the locking bolt, it is ground on a surface grinder and a sine plate (this is an ajustable "angle making" magnetic plate). Given the now machined and ground surfaces, a very close to 100% contact is made by the two parts. Some will suggest replacing the locking bolt, because the rebuilt bolt is imferior. I've yet to see evidence of this. What is fact is that rebuilding the bolt is much more less expensive that a bolt replacement. A new locking bolt comes oversized. Material needs to be removed from the top, bottom, and both sides. Then the angle needs to be added. A new Perazzi bolt is over $100. The fitting of the new bolt could run from $75 to $125. A rebuilt bolt $125. This is because no extra fitting is needed.