Hey Ed -- have had similar problems with my Sebenza. Part of it probably is the difference required in the amount of strength to close the integral vs the average liner lock. Let's face it, it is a much bigger, thicker piece of metal.
But, in addition to that problem, there is the situation where I, at least, used to brace my fingers against the side of the handle, which is now where the lock is located. So, my thumb wasn't only tackling a stronger piece of metal, but it was working against at least a couple fingers to boot.
I've found that it helps me to place my ring and pinky finger sort of hooked around the base of the lock side of the handle -- at the end opposite of the pivot, and hold my social and index fingers sort of out pointing to the side. Then as I push with the thumb, I bring the index finger around behind the end of the blade and push a bit. All that is needed is to get it started, then it is easy. I haven't checked the end of the locking bar for lubricant, but did put a tiny drop of TufGlide down near the detente ball.
My S-2 is even harder than the Sebenza to open. First, the lock goes over half again as far, and there's little doubt it has/requires more power to bend it. Maybe G2 is right, and your bar didn't get heat treated properly.
Good luck!
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