Ficus- new leaves getting discoloured patches

In about the last week, I've noticed the new leaves on my collected ficus (rubiginosa I think, but not sure) are getting pale spots/streaks.

I spray all my plants with a systemic fungicide and insecticide (fluvalinate and myclobutanil) every 2-4 weeks (or whenever I remember) to control scale because a neighbour's hedge is covered in it and it sometimes makes its way to my plants. So, I'm thinking this is either a virus or a nutrient deficiency. I'm leaning towards a nutrient deficiency because it's only affecting the new leaves.

I also noticed that in a small crack between a branch and the trunk, those small black ants are farming mealybugs (those big, white, spikey scale insects). Does this mean a borer or some kind could have gotten in?

A dark ring is also forming around the base of the trunk. The bark has taken on this blackish colour. I scratched some bark back and it's still nice and green underneath it. I don't know how well you can see it in the pictures, but it's more obvious in person.

Here's some pics. Any ideas?

Leaves:








Mealybug hole:



Darkened bark: