I have not had the problem you have described. The Marlins cock on opening the bolt. So it is after you pull the trigger when it becomes difficult to open, as I understand it. Try to lubricate the pin in the back of the bolt. When the bolt is pulled all the way back there is a pin sticking out the bottom of the bolt that rides on the back of the bolt, this is what cocks the firing pin. Make sure this area is smooth too, if it is rough, it will make it difficult to open also. This area that the pin rubs against needs to be lubricated with a good grease. One that is made for guns so it does not gum up or get stiff when cold. If that does not do the trick, I would take the bolt out completely out and give it a through cleaning, paying as much attention as I could to the inside of the bolt, where the firing pin goes, then lightly re lubricate it with a quality gun oil. Remember it is when you are trying to cock it when you have your problem. If you do not pull the trigger, it is already cocked so this action is not needed again until you fire it. Put a already fired case in the chamber and pull the trigger, I bet it becomes difficult to open again because you are trying to re cock the firing pin again. Good Luck and Good Shooting.
