After you have all of the crud off like you said, you can use a 1500 grit sandpaper to buff it up and then switch to 2000. This is very tedious, time consuming work and the sanding has to be done all the way up to each of the frets so there is no variation in finish when you have completed the task.
You won't likely need anything after you finish this lengthy chore, but you could use a dab of lemon oil to rub in if you like.
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