Mr. Chair requests Repair
I've got the sae problem with mine. The web address that everyone gives only supplies replacement bases and swivels, not parts.
I think this is because they used several different mechanisms over the years so individual parts may not exist.
It's the axel-gasket-tube configuration that's gone wrong I think. I believe they've slipped and changed the angle between the set screw and the axel. but I'm guessing. I've dismantled it and tightened the set screw tightly against the outer tube, which works for a while but eventually slips.
The real set screw hole is several degrees over.
I'm about ready to take a drill press to it and create a new set-screw indention.
Any better ideas? Hate to drill on the thing but i can't turn them back. The gasket's too tight.
If what I've said makes sense, or if I'e just missed something entirely and I'm doing it wrong, let me know.
I can take it apart again and get pictures (but it's a kind of PIA and I've done it 5 or 6 times already)