Model 12 slide release sticking

[Dave N]

I recently acquired my grandfather's Model 12 that he had. Never did anything with it until now when I decided I wanted to shoot a rabbit with it. I've had a problem opening the action with it and today I removed the trigger assembly and cleaned it as best as I could without taking it down any more. Plenty of junk in there but it still didn't make any difference. I just can't get the button up enough for it to release. When it IS open I can hold the release up and pump like mad and it moves freely with the slide pulled back. Close the action and it doesn't work. I'm not really planning on shooting it anytime soon and will hang it up on the wall to display but I wouldn't mind having it work correctly for the day it goes to my daughter. Anything I can do or is it a gunsmith issue?