Thanks Chuck. So, next time I have the machine open I'll give that specific stuff a try because apparently the stuff I did just try failed, and... jeeze, Model I's are a PITA to put back together, especially if they have a lot of hack wires running to switches that need to go to randomly positioned holes drilled in the case. I'm going to live with the one edge of the case being a little squishy until I *have* to go back in there.
Long and short of it, I double-checked the chemical shelf in the garage and I found a tin of "Oatey All Purpose Cement" which looked like it might do the job; it's not a pure solvent, it has some polymerizing-stuff in it too, but it said it supported several different plastic types and since I had it I thought it could be worth a shot. And it *looked* like it worked great, the post felt like it was on there to stay after setting for a couple hours and it wasn't obviously turning the case into go, but, no, it let go when the screw was mostly back in, . (Torque is harder than wiggling, apparently.) So, yeah, that's *not* the right answer. I guess if it messed up the mating surfaces a blob of epoxy will probably be the way to go.