The newell post at the top of my staircase has become loose (I suspect from people swinging around it coming downstairs over the years). I can't get at it from below due to the stairs construction. It is oak, as are the stairs, banisters, ballusters, etc. Any suggestions on how to repair it and tighten it back up. I suspect when it was built there was a lag bolt(s) installed up from the bottom.
Many times these newel posts extend below the flooring and are bolted to the framing. If you look at the post, does it look like it's on top on the flooring or is the flooring butted up to the post?
If it's on top, you might try pocket screws and plugs, but the better way would be to manage to get to the attachment under the floor.