I am in the process of updating the trim and moldings in my 1950 home. While outdated molding is easily replaced for doors and floors, my window sills are proving to be quite a problem. The windows were recently replaced, leaving my 10 “ pine sills with what I assume is the remainder of possibly shellac after years of use and leaky windows. I have tried sanding and filling with wood putty to even out the swelling caused by years of condensation, and have used both latex and oil primers (Kilz and Bulls Eye brands), but the pine (yellowing) still bleeds through. Before I give up and just replace them all, can anyone offer some direction from similar experiences?