Depends on the action the gun is built on, but easing them closed may be part of the problem.
You may not be letting the locking parts set all the way. When you fire the gun, this could lead to extra stress/wear on the parts, and a gradual creeping of the toplever.
You should close a SxS or an O/U firmly - not with a flick or a snap, but in one smooth movement. Keep you hand off the toplever. Let the springs and the fitting to its work.
OWD
Absolutely true! If you're going to actually fire the gun then it should be closed as stated above. If merely inspecting/cleaning/admiring, then it's OK to ease the toplever.
The real trick is to try to convince a Smith collector of this.
