When I received it, I loved this chair. However, after owning it for just six months, the connection between the seat and the base, just below the height lever, has come loose. Sitting in the chair now is rather like balancing on a pin, the chair either must lean to one side. I'm not even a large man, just 170lbs. Moreover, the construction is such that I cannot take it apart to fix it. 

As far as I can see, the welds have completely broken. You can see where the square should align, and the beads of steel (welds) no longer align.

Given the expense of the chair, I'm very disappointed. I welcome any communication from the seller or manufacturer.