I got my hands on a Beretta locking block kit (LE9202), one without the spring since my spring seems fine. After disassembling the existing locking block, I discovered someone had inserted the plunger with the wrong orientation and deformed the pin that's supposed to hold it in place. The pin had a slightly bow-like shape, and I could see a shiny spot on the concave surface where the plunger had rubbed against it. I could also see two grooves worn into the plunger where it rubbed against the pin, showing it had been taken out and replaced in a slightly different, but still wrong, orientation. Eventually, the pin became so bent that it could not hold the plunger in place in any orientation. It might have been possible to straighten the pin out and reassemble the existing locking block, but I decided to install the new one and keep the old parts as spares.
It took about 15 minutes to swap the offending parts out for the Beretta kit. Tools required: Hammer, 1/16" punch, and a bit of common sense. I haven't had a chance to shoot it yet, because I am still embroiled in the magazine catch assembly saga.
I have started converting the compatibility list to a spreadsheet so it can be searched, edited, and output into other formats. Unfortunately, life is full of distractions, and I have to prioritize the distractions sent to me by my employer. But I haven't forgotten it.