Since you are a 'mechanical guy', it will be no problem (when you take apart the bottom of the stand) to check if the part which I enclose on the picture is not demaged. It might be the reason why the stand is not functioning as it should. I experienced it once incl. similar symptoms as yours.
The arrows point at two dents in the (plastic) part's ring: they should not be there, instead there should be two square blocks. These broke off (probably while moving the TV) causing the problems. Needless to say it's not an expensive part to change - if this is the problem, of course. Good luck!