What I did was peel back (removed staples) a corner of the liner underneath the chair and closest to the leg.  I reached up in there above the diagonal wood brace that the leg is screwed into. I could feel what I think was the t-nut above the brace.  It was loose and not seated in the brace anymore.  I couldn't reseat it (can't get a hammer in there and no clearance to be able to hammer it back in) but at least I could hold it down and keep it from turning while I screwed the leg into the t-nut.  That worked for me.  Easy peasy