Yellowing leaves have a possible number of reasons why and among them:
not enough light, ...or too much light
not enough fertilizer, or...too much fertilizer
They can also be affected by a nighttime temperature that is too high....they love it in the 60's at night.
Too much water is a common problem causing the leaves---usually the lower ones first, to yellow
Sucking insects such as scale insects, or mealybugs between the stems between the yellowing leves and the roots.
The problem, when corrected, may or may not result in the yellowing leaves to resume their green.

Your benjamina's new growth starts out shiny pale green turning darker green as it matures
but it does like to be fed regularly....when it is growing.
To feed a plant that is not growing can result in problems so be guided by that. Bright light is also appreciated...but we're now just two weeks away from the shortest day of the year....so more light can be given pulling it back as the days get longer.....but later on, no direct sun should be given.
Let the soil dry out between waterings and of course, give no water that is drawn from a softening system....find a tap offline.

Def not too much fertz. Def not too much light. We don't have a water softener as our water is really good here. No bugs, it had spider mites months ago but I sprayed and their gone. I checked yesterday to be sure. I always wait until the soil is dry before watering, that's def not the problem. It's either light (diffused morning sun from northern window) or it's lack of fertilizer.or both. This ficus isn't in the greenhouse so it gets pretty cold at night indoorst (mid-50's at most)

No fertilizer since spring is a pretty clear indicator that your plant is going to be lacking one or more, and I'd bet it is 'several' nutrients, so you should plan on fertilizing. Your plant will scavenge the more mobile nutrients from older organs and use them to fuel new growth when nutritional deficiencies exist, resulting in the shedding of old nutrients. Chill can also be the cause of shedding leaves, as can a reduction in either photo-period or photo-intensity.

The average ACTUAL NPK usage of all plants is approximately 10:1.5:6. That is, for every 10 parts of N your plant uses, it will use about 1.5 parts of P and 6 parts of K. After the factoring is done for how P and K are reported in fertilizers, you'll find that fertilizers with 3:1:2 RATIOs replicate the 10:1.5:6 ratio almost exactly, which indicates some thought was put into fertilizers with 3:1:2 ratios. Ratios are different than NPK %s. Fertilizers with NPK %s of 24-8-16, 12-4-8, and 9-3-6 are all examples of 3:1:2 ratio fertilizers, and would be good choices for your ficus. I use Foliage-Pro 9-3-6 almost exclusively for all my plants, across the board. It would be an excellent choice as your 'go to' fertilizer.

Al