Might need a new lock main spring. It is an old gun from the 70's/80's. Mine are mostly from the 90's and everyone was much improved with a mainspring change.
I have the tool, but usually just GENTLY use a small vice I have mounted. Changing the mainspring...there is more than one way to skin this cat.
https://woodsrunnerstrail.blogspot.com/2011/09/one-hour-gunsmith-puts-new-mainspring.html
Easy to change, easy to find. Deer Creek Products for one. Get the CVA version to avoid inletting issues. They come with a square pin, so you will need to gently use a small fine file to round the pin to fit in the lock hole. It normally take more time to pull all my tools and parts out and put them away than it takes to change a leaf spring in a CVA/Traditions
I have a double handful of high end Spanish SxS sidelock shotguns...they need changing at times also, oft times so much so that gunsmiths make ready replacements to keep in your case with each gun.