Does the pot have drainage holes? Is there a saucer underneath the pot? If so, is there gravel in the saucer to that the pot won't sit in water? If there's no drainage holes, consider a new pot, same size or very slightly bigger. Does the tree get fertilized? If so, could the white stuff be salts/minerals for the water or fertilizer? These trees don't need a lot of fertilizer or an overabundance of water. I don't think I would go as far as removing all of the soil from the roots as long as there's no rot. The more the tree gets disturbed, the more it will pout. I would get a really good potting soil that contains compost (maybe something like Dr. Earth or Happy Frog). Compost is all these trees really need for feeding. Because these trees are in their pots long-term, I would stay away from chemical fertilizers that could have a salt buildup over time. Once the pot and soil issues are resolved, I would spray down the leaves (both sides) with water (outdoors if you want to avoid a mess) - these trees love that. I can't get mine outdoors - too big - so I wash the leaves (both sides) by hand. Once all that's done, misting the plant every couple of days will help with generating new leaves. Facing the bare spot towards the light would be good as long as that sun isn't super strong. My tree has been with me for 25 years and had formerly grown to 10 ft tall in an office building. I cut it down to get it into my house. It's been in the same pot every since with no soil changing - just top-dressing with compost. It will drop some leaves until it gets settled down and, when happy, will produce tiny green fruits (non-edible).
