At the factory, the fellas would close the action, and snap both triggers before returning a gun to the rack. When I asked about tools or snap caps for the case, I was given a wave and a head shake. "So much crap that goes in the case of an English gun. For what?"
I have seen a Darne that had the pin in the percutator fall out, it was just retrieved from the action and pounded back in with a bit of varnish on it. Locktite would work, also. It was/is a mid 1930s Halifax, with an Asian Lt's. name carved into the butt stock, and has seen some use, to say the least. Lt. Quay, I think? Doubt anyone here knows him.
That was the only one. I snap my guns before I return them to the safe. No problems.
Don't dry fire a Darne with the barrels removed from the action. While the older guns have a dove-tailed plate in the front of the action, this gave way to a straight walled plate, retained with two screws from the bottom of the sliding breech. Dry firing the dove-tail guns won't hurt anything, but, it severely stresses the screws in the more modern design. When you dry fire any Darne with the barrels in place, the spring loaded extractor plate supports the face plate of the breech, so, no worries.

Best,
Ted