Tonight I redid the lock sockets on the turntable, and this time they seem to work much better. Before starting, however, I had to get the turntable itself more firmly fixed to the lazy susan base.
To accomplish this, I took the big risk of disassembling everything. Recall that the lazy susan has to be carefully positioned so that it is centered relative to all the tracks that I so carefully laid. I marked it in many places, and removed the lazy susan.
I then re-installed the turntable onto the lazy susan, and ran a couple of pieces of square brass rod up against it as tightly as I could, and soldered them in place. This forms something like a socket to stop the turntable from shifting relative to the lazy susan.
Then tonight, I put everything back together again and went back to soldering the lock sockets onto the lazy susan base. The first five went fine; for some reason the last one took several tries and I’m still not happy with it. I may yet decide to have another go. This was a true test of the forgiveness of solder! It doesn’t look pretty, but it seems to work. Importantly, you can turn the turntable all the way around and return to the same spot again, and lock it in place.