Gents, I appreciate your continued input on this! You bring up some interesting points, but it appears to me:
+ The latch rod is in as far as it will go - plus, it's anchored by a hefty pin that goes completely across the piston body.
+ The seal is likewise socked down as far as possible. I was able to turn the nut "out" a bit, but it won't go "in" any farther than where it started.
In spite of this gun's age (built 1980!), to the best of my knowledge what you see is unaltered factory work. I got it in 1988, from a batch of new guns damaged by a flood in a retail shop (stock finish was a mess but metal fine). It was owned for decades by a friend of mine who probably never put 1000 rounds through it. And he's not an "airgun guy" at all - I'm the only one who's ever poked around inside it, and only to fool with lubes and swapping mainsprings. I'm a bit amazed at how new the guts look.