I am in the process of refinishing/repairing the steps. The top steps are in good shape and I have sanded, applied 1st coat of cetol. See Pictures. I am going to replace the tread piece for the top step, see picture. The PO had the tread in place and I never slipped on the step so I am going to keep it. I am going to fill the other steps groves with either caulk or wood filler as others have done.
Now for the problem, The bottom steps are mounted on plywood and it is separating at the bottom. It will only get worse and need to be replaced. Pictures coming. I looked on the site and cannot find any threads on this repair. I plan on replacing the plywood which will force me to replace screw plugs, new for me. I have also ordered sound proofing from Defender because mine is degrading.