It should not cock if the sear is the wrong way round.
They are easy to strip and check.
I'd strip it and check that there is not a monster mainspring , spacers or "Power washers" , which could lead to it being almost coilbound. The leaf spring in the trigger does not usually give trouble--------but I suppose if it is a coil spring one it might be mangled.
Try swapping mainsprings with your other and see what happens.
Other than that, try polishing and marks out of the holding face of the sear. That can make quite a difference.