Nitrah,
I would not be surprised if a proper strip and clean cured your stiff opening problem. Frankly, my experience with Betts shotguns causes me to question any need for any further work. Betts was a meticulous craftsman, and his shotguns are held in very high esteem because they worked and held up in the shooting fields to whatever conditions they were subjected. IMHO, stiff opening probably isn't a spring problem.......