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Imperial Masterpiece
Seems like really good advice right here!It appears that your tree is just having inner dieback on weak leaves, this is simply because the canopy is so dense and there is no definition. On an aesthetic side having pads of foliage is a nice appearance but on a purely horticulture side creating definition and pads of foliage helps to make sure that all areas of the tree (foliage) gets equal amounts of light.
I can't give you fully true advice as I have no experience growing in your area but in South Florida where I am It is very common for ficus to have mild die back and drop leaves with an extremely dense canopy, especially when it is so crowded like this one.
If this were my tree I would wait until the seasons permit me to do so and then fully defoliate, select branches (I can see many branches you don't need in the final design of the tree), wire til your hands cramp up and pot it up in a slightly larger bulb pan to rebuild.
This could be a very powerful tree if it was shortened a fair bit, and the foliage was redesigned from the current bush/shrub look to something with definition, more tree like. Put the emphasis on that beautiful base and surface roots. That last photo (post 32) looks pretty good!