I found an old, keyless chuck on eBay that I was willing to buy. It was priced almost right (for $25, it should have at least worked). It's a Craftsman keyless chuck from 1972, model 22562 (stamped into the back). it's an integral shank Morse taper (MT1), and when threading on or off, the jaws didn't move. I thought I'd better take it apart and see what the trouble was, since I'm better at taking things apart than I am at putting them back together.
Anyway, before I got it apart, I noticed that some pieces were not lined up when looking through the middle of it. If I pulled the threaded part of the shank out, I could see light through it with a flashlight behind the chuck. I knew it absolutely HAD to come apart.
Some chucks split between the knurled surface on the body and the cone at the top. This one splits between the knurled section and the base (right at the parting line). I had to use some locking wrenches to get it apart. This part took me a while to figure out, since it didn't go the same way as other chucks described out there. Once the body came apart, the whole thing came apart fairly quickly.
It was at this time that I noticed two divots - one in the threaded rod end (between my fingers in the above photo), and one in the piece that was out of place before I got to this point (the round thing in the top-right of the picture - the tweezers are pointing to this part). If this was turned between centers, the slopes on these two divots would be different - they were about a 120-degree cone. It didn't take a genius to realize that I was probably missing a ball bearing. I went out to my stash, and grabbed one that would set in place and allow the two pieces to spin freely of each other.
Then I cleaned it. It felt really tacky to me. A good cleaning, and then I could piece it back together.
The re-assembly went rather quickly, and now I have an old Craftsman keyless drill chuck (circa 1972), MT1, to go with my Craftsman (well, Dunlap) wood lathe (circa 1942).
Looks good, has a slight hang up on retracting a chuck jaw, but it does function. I might need to lightly oil the chuck body (NOT the jaws) to make sure it's good, but I'm happy.