Ivor Johnson Champion hard to cock

[Bessiesboy]

This is a gun I bought used for my son years ago. We both used it at that time and there was no problem. It has been in the back of the gun closet for years and when I got it out to clean and oil it I found it was very difficult to cock the hammer. In fact, since I have lost a bit of strength due to illness I cannot cock it without using a screwdriver to force the hammer back. Two of my friends who are young and strong can cock it but find it very stiff.
I have removed the stock and can see nothing wrong with the parts of the action that are visible. Over the last while it has been oiled and greased and the hammer cycled at least a hundred times, and it still has not loosened up.
There is not a trace of rust visible anywhere that might be binding the action.
The closest gunsmith to my area is about fifty miles away, and I am wondering if anyone here has any suggestions about this nice old gun.
Thanks
Bill