[TARNATION !!!]

Interesting. The only thoughts that come to mind is wear at some point. Is it the duck bill lever spring? If so, is the stub of the spring tight in the hole in the action? Is there any wear on the round top bolt or the square bolt or bolt lever? How about the top lever screw, any damage to the tip end? If it wiggles only when open, it seems the issue has to be with the engagement of the top lever to the slot in the round top bolt. If nothing is worn or broken, I'm stumped.