Age and moisture and possibly rust would be my guess.
At some point I would like to get it apart, but it will probably have to happen the next time I visit a cue repairman.
Meanwhile, I will share what I learned about 'cleaning up' old cues. I purchased this cue because it came with what looked like a nice leather Brunswick case, and because the cue had a Titlist forearm and was beat-up enough that I felt I could refinish it without doing any harm. After a few days in the classifieds in original condition, it was obvious that the cue was not appealing to anyone here, so I went ahead with my plans to clean it up, as follows:
1. Cleaning the wrap - A cuemaker friend described this process over the phone several months ago, and I first tried it on worthless twine wrap, then progressed to a 1910's extremely dirty silk wrap: Pour a little denatured alcohol on a piece of magic eraser, squeeze out most of the liquid, then scrub with the threads (not against). The Courtland wrap on the Palmer was very, very dirty, and had scrapes and scratches that ran down the wrap, so my goal was just to clean off most of the dirt, as opposed to making it look brand new like the example Chris did on his 'Palmercollector' website. After it dried I could better tell what areas needed more work, and once it was fairly even and all the vertical scrapes were gone I quit. I then burnished with a beer glass, rubbing it over a piece of wax paper wrapped around the linen wrap. Then I folded a piece of wax paper a couple of times and burnished the wrap by hand, twisting with the threads until I felt some heat - the effect was that the wax was transferred to the linen wrap. I will post 'before and after' pics in another post in this thread, but the result was what looked like a well cared-for 'used' cue, as opposed to a new cue or an abused cue.
2. Cleaning the forearm - the finish was high-gloss with lots of light and deep scratches, various colors embedded in the scratches from walls, etc. The maple forearm had quite a bit of blue chalk embedded in the grain. For a total refinish of a Hoppe Pro I would have used the magic eraser to scrub off the finish, then added several layers of hand-rubbed finish, depending on what look I was going for. For this one I decided to 'clean' the existing finish, as it was thick and appeared to be original. I started by lightly rubbing the forearm with the magic eraser (with alcohol). The result was simply that the gloss and some of the more superficial damage was removed. I then went a little deeper on the bad abrasions, and scrubbed the part below the joint until almost all the blue was gone. Next I hand-rubbed one coat of Bulls-eye shellac French polish onto the forearm. At that point I stopped, as the level of wear now matched the wrap (in my opinion). The forearm blueing was gone, all color (paint, etc) had been removed from the deeper abrasions, and the lighter abrasions to the finish were gone or very close to it. The cue doesn't look like it has been refinished, just played and taken good care of. It could probably use one more coat of Bullseye.
3. Shaft - the shaft was warped and the tip lifted. I decided to try and straighten it using a technique described to me by a cue repairman on this forum. I got most of the bend out of it and the tip no longer lifts. I showed it to someone who has experience with straightening shafts and he did a little more work on it. The result was a nice-hitting cue, so I stopped. I then cleaned the shaft using a magic eraser, then burnished with leather, then applied Renaissance wax and burnished that with a piece of brown paper bag.
4. The Butt - as described at the beginning of this thread, I can't get the weight bolt to budge; however, I expect a local cue repairman to be able to take care of it. The last step will be analyzing the interior and deciding what to do next.