I have a span of 16 feet on an existing garage door opening. The header sagged in the middle 2 inches over a period of 26 years. The added chain automated garage door opener (wooden door) still works but the panels are starting to separate. There are two stories above the door and double hung windows above are skewed accordingly. The counterbalance spring for the door runs length-wise across the top of the opening. The door can be manually opened using two fingers so binding is not a problem. Over the past several months I have jacked up the center 1/4" per month with no noticable cracks on that wall above the door. I'm now at the "What do I do now?" stage. I'm thinking a steel beam would do the job but not sure how to remove old wood and slide in the iron work. Also I will not tackle that spring unless I know exactly what I'm doing. (Death is natures way of telling you to slow down!). I'm tool-loaded, renovation experienced, and not afraid to learn the right way to do a job. Any help out there?