Take the action out of the stock and you can see the trigger mechanism pretty easily, it shouldn't be too hard to trip the top sear that holds the piston rod back, I've not really heard of the triggers falling apart but I know the pins that hold all the mechanism together can come out if the action isn't put back in the stock carefully but the stock normally holds them in once put back in, there is a small conical spring that goes behind the piston sear, that may need looking at.
Pete