I had this free dining chair in terrible shape. Layers of old finishes, candle wax dripped on it, cane bottom long since gone and replaced with a poorly fitted fake leather over a cardboard-like seat. Oh, and all the glue joints were loose, some even had old nails trying to keep it together. It was a beautiful chair though, quartersawn white oak.

I knocked it all apart (mostly round mortise & tenons, some elongated ones for the pressed back etc.) and stripped the old finish, then reglued it all back together with good wood glue and clamps. Then redid the cane bottom. It was fine at first but after only a few sittings, the glue joints began to come loose.

Is it possible there is old finish or glue on the mortises and tenons? I don't remember the tenons being cruddy. If I sanded the tenons and drilled out the mortises, wouldn't they no longer fit snugly and would be loose anyway? How do you fix this?