I own 3 GT's 1 Auto and 2 Manuals
I don't use my knives hard but have not had any problems with the button lock. I have also taken them apart to clean, very simple design. The knive is locked in place by two elevated metal pins attached to the button mechanism which lock into the blade.
The only bad thing is, however, I purchased my first one manual about 1 - 1 1/2 years ago great solid knive. By second Menual I purched off of E-bay NIB never used. I had to take it apart and fix some problem with the locking mechanism, one of the srews was stripped and the feel of the knife is not smooth. Even after I worked on the knife it still does not compare to my First manual. I have had no problems with my Auto. I like them but feel the quality has gone down over the last year conciderably.
Hope this if help some
Wolf