refinishing press back oak chairs

I just received 6 press back oak chairs. Because of the uneveness of the previous owner's slate floor the chair legs have become loose, some of the rungs are broken and will need to be replaced.
Two of the chairs I can use for "parts" to repair the other 4 chairs. One of the chairs looks brand new - the finish still shines brightly. The remaining chairs are worn or have scratches and are dingy looking from being stored in a garage. What would be the best way to liven up the finish or restore these chairs.

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