I have also found that most of these are poorly made and abused so they are doomed to failure. As you know, they are basically a geared interface, radial teeth that should mate with grooves on the other side of the interface. Very shallow and, as said above, only at discreet points such as "just under 10deg". But original manufacture of those teeth and grooves is often poorly done or the teeth are badly damaged with use and so cannot mate with the grooves very well and so it slips. Poor mating at one point weakens the interface so it slips a bit and damages other sectors, so it slips and damages other sectors, until you, practically, have no more than a mashed together fit, no geared engagement. And the tooth/groove engagement is probably not "clocked" the same, side to side, so it's all a fools errand. Scrap.
I have had some success with taking a pretty good clamp apart and dressing all the teeth, all four faces, with a file or a rotary tool to clean up the grooves and teeth. Get rid of any buggered up metal leaving clean ridges. Then put it back together and carefully set the saddle angle you want and tighten it up very tight. Avoid that very first rotation after that as just a bit of rotation will "smear" some metal and start the problem all over again.
Or get a Campy two bolt seat post.