The top lever spring will not go "soft", it is tempered. Either it works or it doesn't. Now it could be broken, but then there would be no tension at all on the top lever and the only thing keeping it in the open position is the top lever trip and the spring underneath it. If Rolf's tension is still there on the top lever then the trip lever spring is either broken or the coils are weak.
Make sure that the little screw in front of the trigger guard in the trigger plate housing is still there or else the top lever will move very hard and will have risen up some.