At 18-years, you are beyond the norm for replacement of the whole thing. But, some do last a lot longer. Depends somewhat on luck of the draw and the quality of the water. If you have an impact wrench, you should be able to get the old rod out, a breaker bar may not do it. Then, depending on the available height above it, you may need to buy a segmented replacement rod rather than a solid one. It's a tossup now, as the old rod is probably used up, and any impact may open up additional opportunities for it to then start leaking. Depends on how lucky you feel.
Draining helps by removing any debris and maintaining the heating and volume of hot water you can get from the tank, but probably doesn't do much to extend the useful life from leaking.