I then discovered that the manual recommends loosening the screw frequently to keep it from getting stuck. I also found out from searching the WWW that this is a common problem, & some people recommend replacing the original screw with a hex head screw of the same thread.
I gave up & ordered a new soldering iron (just the iron itself, to plug into the base), which should arrive any day now. I don't want to ruin another one, so...
Should I grease the screw threads with something to prevent sticking (& if so, what) or will anything on the threads end up getting cooked & making it jam up? (Stuff I have in stock in the house includes silicone grease, very old lithium grease, & some copper-based stuff for keeping threads on bike components from freezing, as well as the usual WD40.)
Should I just loosen the screw after every use & store it that way?
Is there any reason not to replace the set screw that goes all the way into the tip-holder with a screw with the same thread but a head (with a hex hole) that will sit outside the tip-holder of the iron?